Improve Chunk Prioritization and Internal Scheduler

In previous MC versions, we had a rather simple internal scheduler
for delayed tasks that would just keep pushing task back until desired
tick was reached.

The method it called to schedule the task changed behavior in 1.14, and now
this scheduler is not working nowhere near what it was supposed to be doing.

This was causing long delayed task to eat up CPU (In Oversleep for example)

Rewrite this to just use the CraftScheduler for scheduling delayed tasks.

Once this was fixed, it became quite clear the code that delayed ticket
additions for chunks based on distance was clearly not right, as it was
tested on the previous broken logic.

So the ticket delay process has been vastly revamped to be even smarter.
Chunks behind the player can load slower than the chunks in front of the player.
We also can delay ticket adding until one of its neighbors has loaded, as
this lets us get a smoother spiral out for the chunks (minus frustum intent).

Additionally on frustum previous commit inadvertently broke frustum trying to
fix an issue when the real fix lied elsewhere, so restore chunk priority so
it works again.

Spigot-Server-Patches/MC-Utils.patch

@@ -3568,30 +3568,12 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +        return MinecraftServer.getServer().isMainThread();
 +    }
 +
-+    private static class DelayedRunnable implements Runnable {
-+
-+        private final int ticks;
-+        private final Runnable run;
-+
-+        private DelayedRunnable(int ticks, Runnable run) {
-+            this.ticks = ticks;
-+            this.run = run;
-+        }
-+
-+        @Override
-+        public void run() {
-+            if (ticks <= 0) {
-+                run.run();
-+            } else {
-+                scheduleTask(ticks-1, run);
-+            }
-+        }
++    public static org.bukkit.scheduler.BukkitTask scheduleTask(int ticks, Runnable runnable) {
++        return scheduleTask(ticks, runnable, null);
 +    }
 +
-+    public static void scheduleTask(int ticks, Runnable runnable) {
-+        // We use post to main instead of process queue as we don't want to process these mid tick if
-+        // Someone uses processQueueWhileWaiting
-+        MinecraftServer.getServer().scheduleOnMain(new DelayedRunnable(ticks, runnable));
++    public static org.bukkit.scheduler.BukkitTask scheduleTask(int ticks, Runnable runnable, String taskName) {
++        return MinecraftServer.getServer().server.getScheduler().scheduleInternalTask(runnable, ticks, taskName);
 +    }
 +
 +    public static void processQueue() {
@@ -4495,6 +4477,194 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
  
      /**
       * Mirror
+diff --git a/src/main/java/org/bukkit/craftbukkit/scheduler/CraftScheduler.java b/src/main/java/org/bukkit/craftbukkit/scheduler/CraftScheduler.java
+index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
+--- a/src/main/java/org/bukkit/craftbukkit/scheduler/CraftScheduler.java
++++ b/src/main/java/org/bukkit/craftbukkit/scheduler/CraftScheduler.java
+@@ -0,0 +0,0 @@ import org.bukkit.scheduler.BukkitWorker;
+  */
+ public class CraftScheduler implements BukkitScheduler {
+ 
++    static Plugin MINECRAFT = new MinecraftInternalPlugin();
+     /**
+      * Counter for IDs. Order doesn't matter, only uniqueness.
+      */
+@@ -0,0 +0,0 @@ public class CraftScheduler implements BukkitScheduler {
+         runTaskTimer(plugin, (Object) task, delay, period);
+     }
+ 
++    public BukkitTask scheduleInternalTask(Runnable run, int delay, String taskName) {
++        final CraftTask task = new CraftTask(run, nextId(), taskName);
++        return handle(task, delay);
++    }
++
+     public BukkitTask runTaskTimer(Plugin plugin, Object runnable, long delay, long period) {
+         validate(plugin, runnable);
+         if (delay < 0L) {
+diff --git a/src/main/java/org/bukkit/craftbukkit/scheduler/CraftTask.java b/src/main/java/org/bukkit/craftbukkit/scheduler/CraftTask.java
+index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
+--- a/src/main/java/org/bukkit/craftbukkit/scheduler/CraftTask.java
++++ b/src/main/java/org/bukkit/craftbukkit/scheduler/CraftTask.java
+@@ -0,0 +0,0 @@ public class CraftTask implements BukkitTask, Runnable { // Spigot
+     CraftTask(final Object task) {
+         this(null, task, CraftTask.NO_REPEATING, CraftTask.NO_REPEATING);
+     }
++    // Paper start
++    public String taskName = null;
++    boolean internal = false;
++    CraftTask(final Object task, int id, String taskName) {
++        this.rTask = (Runnable) task;
++        this.cTask = null;
++        this.plugin = CraftScheduler.MINECRAFT;
++        this.taskName = taskName;
++        this.internal = true;
++        this.id = id;
++        this.period = CraftTask.NO_REPEATING;
++        this.taskName = taskName;
++        this.timings = null; // Will be changed in later patch
++    }
++    // Paper end
+ 
+     CraftTask(final Plugin plugin, final Object task, final int id, final long period) {
+         this.plugin = plugin;
+diff --git a/src/main/java/org/bukkit/craftbukkit/scheduler/MinecraftInternalPlugin.java b/src/main/java/org/bukkit/craftbukkit/scheduler/MinecraftInternalPlugin.java
+new file mode 100644
+index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000
+--- /dev/null
++++ b/src/main/java/org/bukkit/craftbukkit/scheduler/MinecraftInternalPlugin.java
+@@ -0,0 +0,0 @@
++package org.bukkit.craftbukkit.scheduler;
++
++
++import org.bukkit.Server;
++import org.bukkit.command.Command;
++import org.bukkit.command.CommandSender;
++import org.bukkit.configuration.file.FileConfiguration;
++import org.bukkit.generator.ChunkGenerator;
++import org.bukkit.plugin.PluginBase;
++import org.bukkit.plugin.PluginDescriptionFile;
++import org.bukkit.plugin.PluginLoader;
++import org.bukkit.plugin.PluginLogger;
++
++import java.io.File;
++import java.io.InputStream;
++import java.util.List;
++
++public class MinecraftInternalPlugin extends PluginBase {
++    private boolean enabled = true;
++
++    private final String pluginName;
++    private PluginDescriptionFile pdf;
++
++    public MinecraftInternalPlugin() {
++        this.pluginName = "Minecraft";
++        pdf = new PluginDescriptionFile(pluginName, "1.0", "nms");
++    }
++
++    public void setEnabled(boolean enabled) {
++        this.enabled = enabled;
++    }
++
++    @Override
++    public File getDataFolder() {
++        throw new UnsupportedOperationException("Not supported.");
++    }
++
++    @Override
++    public PluginDescriptionFile getDescription() {
++        return pdf;
++    }
++
++    @Override
++    public FileConfiguration getConfig() {
++        throw new UnsupportedOperationException("Not supported.");
++    }
++
++    @Override
++    public InputStream getResource(String filename) {
++        throw new UnsupportedOperationException("Not supported.");
++    }
++
++    @Override
++    public void saveConfig() {
++        throw new UnsupportedOperationException("Not supported.");
++    }
++
++    @Override
++    public void saveDefaultConfig() {
++        throw new UnsupportedOperationException("Not supported.");
++    }
++
++    @Override
++    public void saveResource(String resourcePath, boolean replace) {
++        throw new UnsupportedOperationException("Not supported.");
++    }
++
++    @Override
++    public void reloadConfig() {
++        throw new UnsupportedOperationException("Not supported.");
++    }
++
++    @Override
++    public PluginLogger getLogger() {
++        throw new UnsupportedOperationException("Not supported.");
++    }
++
++    @Override
++    public PluginLoader getPluginLoader() {
++        throw new UnsupportedOperationException("Not supported.");
++    }
++
++    @Override
++    public Server getServer() {
++        throw new UnsupportedOperationException("Not supported.");
++    }
++
++    @Override
++    public boolean isEnabled() {
++        return enabled;
++    }
++
++    @Override
++    public void onDisable() {
++        throw new UnsupportedOperationException("Not supported.");
++    }
++
++    @Override
++    public void onLoad() {
++        throw new UnsupportedOperationException("Not supported.");
++    }
++
++    @Override
++    public void onEnable() {
++        throw new UnsupportedOperationException("Not supported.");
++    }
++
++    @Override
++    public boolean isNaggable() {
++        throw new UnsupportedOperationException("Not supported.");
++    }
++
++    @Override
++    public void setNaggable(boolean canNag) {
++        throw new UnsupportedOperationException("Not supported.");
++    }
++
++    @Override
++    public ChunkGenerator getDefaultWorldGenerator(String worldName, String id) {
++        throw new UnsupportedOperationException("Not supported.");
++    }
++
++    @Override
++    public boolean onCommand(CommandSender sender, Command command, String label, String[] args) {
++        throw new UnsupportedOperationException("Not supported.");
++    }
++
++    @Override
++    public List<String> onTabComplete(CommandSender sender, Command command, String alias, String[] args) {
++        throw new UnsupportedOperationException("Not supported.");
++    }
++}
 diff --git a/src/main/java/org/bukkit/craftbukkit/util/DummyGeneratorAccess.java b/src/main/java/org/bukkit/craftbukkit/util/DummyGeneratorAccess.java
 index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
 --- a/src/main/java/org/bukkit/craftbukkit/util/DummyGeneratorAccess.java