Rewrite chunk system (#8177)

Patch documentation to come

Issues with the old system that are fixed now:
- World generation does not scale with cpu cores effectively.
- Relies on the main thread for scheduling and maintaining chunk state, dropping chunk load/generate rates at lower tps.
- Unreliable prioritisation of chunk gen/load calls that block the main thread.
- Shutdown logic is utterly unreliable, as it has to wait for all chunks to unload - is it guaranteed that the chunk system is in a state on shutdown that it can reliably do this? Watchdog shutdown also typically failed due to thread checks, which is now resolved.
- Saving of data is not unified (i.e can save chunk data without saving entity data, poses problems for desync if shutdown is really abnormal.
- Entities are not loaded with chunks. This caused quite a bit of headache for Chunk#getEntities API, but now the new chunk system loads entities with chunks so that they are ready whenever the chunk loads in. Effectively brings the behavior back to 1.16 era, but still storing entities in their own separate regionfiles.

The above list is not complete. The patch documentation will complete it.

New chunk system hard relies on starlight and dataconverter, and most importantly the new concurrent utilities in ConcurrentUtil.

Some of the old async chunk i/o interface (i.e the old file io thread reroutes _some_ calls to the new file io thread) is kept for plugin compat reasons. It will be removed in the next major version of minecraft.

The old legacy chunk system patches have been moved to the removed folder in case we need them again.

patches/server/0127-Properly-fix-item-duplication-bug.patch

@@ -1,33 +0,0 @@
-From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
-From: Alfie Cleveland <alfeh@me.com>
-Date: Tue, 27 Dec 2016 01:57:57 +0000
-Subject: [PATCH] Properly fix item duplication bug
-
-Credit to prplz for figuring out the real issue
-
-diff --git a/src/main/java/net/minecraft/server/level/ServerPlayer.java b/src/main/java/net/minecraft/server/level/ServerPlayer.java
-index 4d8dfe375f5b3b9e5cfc12a6af0b87ae78f9b764..5d214b7dd4f6d7feff0a1904ce6573cffd258a1c 100644
---- a/src/main/java/net/minecraft/server/level/ServerPlayer.java
-+++ b/src/main/java/net/minecraft/server/level/ServerPlayer.java
-@@ -2210,7 +2210,7 @@ public class ServerPlayer extends Player {
- 
-     @Override
-     public boolean isImmobile() {
--        return super.isImmobile() || !this.getBukkitEntity().isOnline();
-+        return super.isImmobile() || (this.connection != null && this.connection.isDisconnected()); // Paper
-     }
- 
-     @Override
-diff --git a/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java b/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
-index 75bc0d9e8ec46d1fcfd6d5886d5ab03537e575d2..9df3561fca35b1649de1545e924bd96ec5f80089 100644
---- a/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
-+++ b/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
-@@ -3283,7 +3283,7 @@ public class ServerGamePacketListenerImpl implements ServerPlayerConnection, Tic
-     }
- 
-     public final boolean isDisconnected() {
--        return !this.player.joining && !this.connection.isConnected();
-+        return (!this.player.joining && !this.connection.isConnected()) || this.processedDisconnect; // Paper
-     }
-     // CraftBukkit end
-