Make loadChunksAsync callback thread-safe

Need to perform synchronisation on the return list to avoid CMEs

patches/server/0024-Make-loadChunksAsync-callback-thread-safe.patch

@@ -0,0 +1,21 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Spottedleaf <[email protected]>
+Date: Tue, 25 Jul 2023 11:47:18 -0700
+Subject: [PATCH] Make loadChunksAsync callback thread-safe
+
+Need to perform synchronisation on the return list to avoid CMEs
+
+diff --git a/src/main/java/net/minecraft/server/level/ServerLevel.java b/src/main/java/net/minecraft/server/level/ServerLevel.java
+index 60b409e873d8f5d7975cce6e86ee2ed5525d348c..cf8f93734121e5c1959959f0ba13ee4e6db31959 100644
+--- a/src/main/java/net/minecraft/server/level/ServerLevel.java
++++ b/src/main/java/net/minecraft/server/level/ServerLevel.java
+@@ -347,7 +347,9 @@ public class ServerLevel extends Level implements WorldGenLevel {
+
+         java.util.function.Consumer<net.minecraft.world.level.chunk.ChunkAccess> consumer = (net.minecraft.world.level.chunk.ChunkAccess chunk) -> {
+             if (chunk != null) {
++                synchronized (ret) { // Folia - region threading - make callback thread-safe TODO rebase
+                 ret.add(chunk);
++                } // Folia - region threading - make callback thread-safe TODO rebase
+                 chunkProvider.addTicketAtLevel(TicketType.FUTURE_AWAIT, chunk.getPos(), ticketLevel, holderIdentifier);
+             }
+             if (loadedChunks.incrementAndGet() == requiredChunks) {