Rework async chunk api implementation

Firstly, the old methods all routed to the CompletableFuture method.
However, the CF method could not guarantee that if the caller
was off-main that the future would be "completed" on-main. Since
the callback methods used the CF one, this meant that the callback
methods did not guarantee that the callbacks were to be called on
the main thread.

Now, all methods route to getChunkAtAsync(x, z, gen, urgent, cb)
so that the methods with the callback are guaranteed to invoke
the callback on the main thread. The CF behavior remains unchanged;
it may still appear to complete on main if invoked off-main.

Secondly, remove the scheduleOnMain invocation in the async
chunk completion. This unnecessarily delays the callback
by 1 tick.

Thirdly, add getChunksAtAsync(minX, minZ, maxX, maxZ, ...) which
will load chunks within an area. This method is provided as a helper
as keeping all chunks loaded within an area can be complicated to
implement for plugins (due to the lacking ticket API), and is
already implemented internally anyways.

Fourthly, remove the ticket addition that occured with getChunkAt
and getChunkAtAsync. The ticket addition may delay the unloading
of the chunk unnecessarily. It also fixes a very rare timing bug
where the future/callback would be completed after the chunk
unloads.

patches/server/0310-Add-debug-for-sync-chunk-loads.patch

@@ -314,10 +314,10 @@ index 758b874424b1fed90893132e5455a683b789ebf2..0a895055ec7f61d3cb52d303bbe3f894
              ChunkAccess ichunkaccess1 = (ChunkAccess) chunkresult.orElse(null); // CraftBukkit - decompile error
  
 diff --git a/src/main/java/net/minecraft/server/level/ServerLevel.java b/src/main/java/net/minecraft/server/level/ServerLevel.java
-index 800dd7338d77289b7d0e6e126342eaea184d3e43..ecb9f6f0c9b24313b9e55b3a4c4f4bba40bc8fb3 100644
+index 32117fe89ca946658a7d292b4a470736a09bfa62..af3adf1bf771c2327b2972a4f9db9df4c4775f1a 100644
 --- a/src/main/java/net/minecraft/server/level/ServerLevel.java
 +++ b/src/main/java/net/minecraft/server/level/ServerLevel.java
-@@ -410,6 +410,13 @@ public class ServerLevel extends Level implements ServerEntityGetter, WorldGenLe
+@@ -415,6 +415,13 @@ public class ServerLevel extends Level implements ServerEntityGetter, WorldGenLe
          this.getCraftServer().addWorld(this.getWorld()); // CraftBukkit
      }