Implement Chunk Priority / Urgency System for Chunks

Mark chunks that are blocking main thread for world generation as urgent

Implements a general priority system so that chunks that are sorted in
the generator queues can prioritize certain chunks over another.

Urgent chunks will jump to the front of the line, ensuring that a
sync chunk load on an ungenerated chunk does not lag the server for
a long period of time if the servers generator queues are filled with
lots of chunks already.

This massively reduces the lag spikes from sync chunk gens.

Then we further prioritize loading order so nearby chunks have higher
priority than distant chunks, reducing the pressure a high no tick
view distance holds on you.

Chunks in front of the player have higher priority, to help with
fast traveling players keep up with their movement.

This commit also improves single core cpu scenarios in that we will
now automatically disable Async Chunks as well as Minecrafts thread
pool.

It is never recommended to use async chunks on a single CPU as context
switching will be slower than just running it all on main.

This also bumps the number of server worker threads by default too.
Mojang does not utilize the workers in an effecient manner, resulting
in them using barely any sustained CPU.

So give it more workers so more chunks can be processed concurrently

This change also improves urgent chunk loading, so players flying into
unloaded chunks will hurt a little bit less (but still hurt)

Ping #3395 #3363 (Not marking as closed, we need to make prevent moving work)

Spigot-Server-Patches/0154-Basic-PlayerProfile-API.patch

@@ -403,7 +403,7 @@ index 0000000000000000000000000000000000000000..3aceb0ea8a1a3ed94dd8a9e954c52ecd
 +    }
 +}
 diff --git a/src/main/java/net/minecraft/server/MCUtil.java b/src/main/java/net/minecraft/server/MCUtil.java
-index 87bd51ab1b844e05ecd3d9d2555841554976023c..37b8257552efd0d66a020f0b5007514f2ac890cd 100644
+index f9a7a1e9eea67bafb85c0ed88e96abb8e45f6c81..8ca1a4719d934db31d57b34cf7050acc5a1a7048 100644
 --- a/src/main/java/net/minecraft/server/MCUtil.java
 +++ b/src/main/java/net/minecraft/server/MCUtil.java
 @@ -1,7 +1,10 @@
@@ -417,7 +417,7 @@ index 87bd51ab1b844e05ecd3d9d2555841554976023c..37b8257552efd0d66a020f0b5007514f
  import org.apache.commons.lang.exception.ExceptionUtils;
  import org.bukkit.Location;
  import org.bukkit.block.BlockFace;
-@@ -315,6 +318,10 @@ public final class MCUtil {
+@@ -329,6 +332,10 @@ public final class MCUtil {
          return run.get();
      }