Optimize Network Manager to not need synchronization

Removes synchronization from sending packets
Makes normal packet sends no longer need to be wrapped and queued like it use to work.
Adds more packet queue immunities on top of keep alive to let the following scenarios go out
without delay:
  - Keep Alive
  - Chat
  - Kick
  - All of the packets during the Player Joined World event

Hoping that latter one helps join timeout issues more too for slow connections.

Removes processing packet queue off of main thread
  - for the few cases where it is allowed, order is not necessary nor
    should it even be happening concurrently in first place (handshaking/login/status)

Ensures packets sent asynchronously are dispatched on main thread

This helps ensure safety for ProtocolLib as packet listeners
are commonly accessing world state. This will allow you to schedule
a packet to be sent async, but itll be dispatched sync for packet
listeners to process.

This should solve some deadlock risks

This may provide a decent performance improvement because thread synchronization incurs a cache reset
so by avoiding ever entering a synchronized block, we get to avoid that, and packet sending is a really
hot activity.

Spigot-Server-Patches/Optimize-PlayerChunkMap-memory-use-for-visibleChunks.patch

@@ -13,7 +13,7 @@ This should result in siginificant memory use reduction and improved GC behavior
 
 diff --git a/src/main/java/com/destroystokyo/paper/util/map/Long2ObjectLinkedOpenHashMapFastCopy.java b/src/main/java/com/destroystokyo/paper/util/map/Long2ObjectLinkedOpenHashMapFastCopy.java
 new file mode 100644
-index 0000000000..e0ad725b2e
+index 00000000000..e0ad725b2e6
 --- /dev/null
 +++ b/src/main/java/com/destroystokyo/paper/util/map/Long2ObjectLinkedOpenHashMapFastCopy.java
 @@ -0,0 +0,0 @@
@@ -50,7 +50,7 @@ index 0000000000..e0ad725b2e
 +    }
 +}
 diff --git a/src/main/java/net/minecraft/server/ChunkProviderServer.java b/src/main/java/net/minecraft/server/ChunkProviderServer.java
-index ca1b5b3b09..c457e3b772 100644
+index ca1b5b3b094..c457e3b772e 100644
 --- a/src/main/java/net/minecraft/server/ChunkProviderServer.java
 +++ b/src/main/java/net/minecraft/server/ChunkProviderServer.java
 @@ -0,0 +0,0 @@ public class ChunkProviderServer extends IChunkProvider {
@@ -63,7 +63,7 @@ index ca1b5b3b09..c457e3b772 100644
  
                  if (optional.isPresent()) {
 diff --git a/src/main/java/net/minecraft/server/MCUtil.java b/src/main/java/net/minecraft/server/MCUtil.java
-index d9941b38ca..71ab65e00f 100644
+index d9941b38ca0..71ab65e00fe 100644
 --- a/src/main/java/net/minecraft/server/MCUtil.java
 +++ b/src/main/java/net/minecraft/server/MCUtil.java
 @@ -0,0 +0,0 @@ public final class MCUtil {
@@ -76,7 +76,7 @@ index d9941b38ca..71ab65e00f 100644
              List<PlayerChunk> allChunks = new ArrayList<>(visibleChunks.values());
              List<EntityPlayer> players = world.players;
 diff --git a/src/main/java/net/minecraft/server/PlayerChunkMap.java b/src/main/java/net/minecraft/server/PlayerChunkMap.java
-index e22ef19534..db5a35598d 100644
+index 4beae504c87..00f26ae23da 100644
 --- a/src/main/java/net/minecraft/server/PlayerChunkMap.java
 +++ b/src/main/java/net/minecraft/server/PlayerChunkMap.java
 @@ -0,0 +0,0 @@ public class PlayerChunkMap extends IChunkLoader implements PlayerChunk.d {
@@ -213,7 +213,7 @@ index e22ef19534..db5a35598d 100644
          while (objectbidirectionaliterator.hasNext()) {
              Entry<PlayerChunk> entry = (Entry) objectbidirectionaliterator.next();
 diff --git a/src/main/java/org/bukkit/craftbukkit/CraftWorld.java b/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
-index 07ebd78acc..b70c0fd977 100644
+index 07ebd78acc7..b70c0fd977c 100644
 --- a/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
 +++ b/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
 @@ -0,0 +0,0 @@ import net.minecraft.server.GameRules;