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/0382-Prevent-Double-PlayerChunkMap-adds-crashing-server.patch

@@ -1,48 +0,0 @@
-From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
-From: Aikar <aikar@aikar.co>
-Date: Thu, 2 Apr 2020 01:42:39 -0400
-Subject: [PATCH] Prevent Double PlayerChunkMap adds crashing server
-
-Suspected case would be around the technique used in .stopRiding
-Stack will identify any causer of this and warn instead of crashing.
-
-diff --git a/src/main/java/net/minecraft/server/level/ChunkMap.java b/src/main/java/net/minecraft/server/level/ChunkMap.java
-index 9e940920f6ff6a43d7162d965936c171c55ed570..72af82374f47a1effc3d2f45beee1f611b4bb4b6 100644
---- a/src/main/java/net/minecraft/server/level/ChunkMap.java
-+++ b/src/main/java/net/minecraft/server/level/ChunkMap.java
-@@ -1754,6 +1754,14 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
- 
-     public void addEntity(Entity entity) {
-         org.spigotmc.AsyncCatcher.catchOp("entity track"); // Spigot
-+        // Paper start - ignore and warn about illegal addEntity calls instead of crashing server
-+        if (!entity.valid || entity.level != this.level || this.entityMap.containsKey(entity.getId())) {
-+            new Throwable("[ERROR] Illegal PlayerChunkMap::addEntity for world " + this.level.getWorld().getName()
-+                + ": " + entity  + (this.entityMap.containsKey(entity.getId()) ? " ALREADY CONTAINED (This would have crashed your server)" : ""))
-+                .printStackTrace();
-+            return;
-+        }
-+        // Paper end
-         if (!(entity instanceof EnderDragonPart)) {
-             EntityType<?> entitytypes = entity.getType();
-             int i = entitytypes.clientTrackingRange() * 16;
-diff --git a/src/main/java/net/minecraft/server/level/ServerLevel.java b/src/main/java/net/minecraft/server/level/ServerLevel.java
-index ed8014ed36f8354aa1ae07689e9315c0c0d8867a..f5a9edf47230a1552a36ee5de4cb7560ea9ba7c4 100644
---- a/src/main/java/net/minecraft/server/level/ServerLevel.java
-+++ b/src/main/java/net/minecraft/server/level/ServerLevel.java
-@@ -2294,7 +2294,7 @@ public class ServerLevel extends Level implements WorldGenLevel {
- 
-         public void onTrackingStart(Entity entity) {
-             org.spigotmc.AsyncCatcher.catchOp("entity register"); // Spigot
--            ServerLevel.this.getChunkSource().addEntity(entity);
-+            // ServerLevel.this.getChunkSource().addEntity(entity); // Paper - moved down below valid=true
-             if (entity instanceof ServerPlayer) {
-                 ServerPlayer entityplayer = (ServerPlayer) entity;
- 
-@@ -2328,6 +2328,7 @@ public class ServerLevel extends Level implements WorldGenLevel {
- 
-             entity.updateDynamicGameEventListener(DynamicGameEventListener::add);
-             entity.valid = true; // CraftBukkit
-+            ServerLevel.this.getChunkSource().addEntity(entity);
-             // Paper start - Set origin location when the entity is being added to the world
-             if (entity.getOriginVector() == null) {
-                 entity.setOrigin(entity.getBukkitEntity().getLocation());