Add RegistryAccess for managing Registries

RegistryAccess is independant from CraftServer and
doesn't require one to be created allowing the
org.bukkit.Registry class to be loaded earlier.

== AT ==
public net.minecraft.server.RegistryLayer STATIC_ACCESS

paper-server/src/main/java/io/papermc/paper/util/Holderable.java

@@ -0,0 +1,14 @@
+package io.papermc.paper.util;
+
+import net.minecraft.core.Holder;
+import org.bukkit.craftbukkit.util.Handleable;
+
+public interface Holderable<M> extends Handleable<M> {
+
+    Holder<M> getHolder();
+
+    @Override
+    default M getHandle() {
+        return this.getHolder().value();
+    }
+}