Modify CraftWorld#getChunkAt(x, z) to functional by sync operation.

[ColdeZhang]

When I was using getForceLoadedChunks() it throw:

[21:44:53 ERROR]: [ca.spottedleaf.moonrise.common.util.TickThread] Thread Region Scheduler Thread #2 failed main thread check: Async chunk retrieval
java.lang.Throwable: null
        at ca.spottedleaf.moonrise.common.util.TickThread.ensureTickThread(TickThread.java:51) ~[deerfolia-1.21.4.jar:1.21.4-DEV-2bd64a2]
        at org.bukkit.craftbukkit.CraftWorld.getChunkAt(CraftWorld.java:373) ~[deerfolia-1.21.4.jar:1.21.4-DEV-2bd64a2]
        at org.bukkit.craftbukkit.CraftWorld.getForceLoadedChunks(CraftWorld.java:690) ~[deerfolia-1.21.4.jar:1.21.4-DEV-2bd64a2]

If getChunkAt forced ensureTickThread, then other api wont get proper reult forever.

Since this method was a 'read-only', why don't we just sync it to get what we want?

[ColdeZhang]

    @Override
    public Chunk getChunkAt(int x, int z) {
        net.minecraft.world.level.chunk.LevelChunk chunk;
        try {
            if (((ServerLevel) world).regioniser.getRegionAtUnsynchronised(x >> 4, z >> 4) != null)
                ((ServerLevel) world).regioniser.getRegionAtUnsynchronised(x >> 4, z >> 4).regioniser.acquireReadLock(); // Folia - region threading
            warnUnsafeChunk("getting a faraway chunk", x, z); // Paper
            chunk = (net.minecraft.world.level.chunk.LevelChunk) this.world.getChunk(x, z, ChunkStatus.FULL, true);
        } catch (Exception e) {
            throw new RuntimeException(e);
        } finally {
            if (((ServerLevel) world).regioniser.getRegionAtUnsynchronised(x >> 4, z >> 4) != null)
                ((ServerLevel) world).regioniser.getRegionAtUnsynchronised(x >> 4, z >> 4).regioniser.releaseReadLock(); // Folia - region threading
        }
        return new CraftChunk(chunk);
    }

[PedroMPagani]

That's not a proper solution, you should never call getChunk with possibility of loading it like that, it's a blocking call.

[masmc05]

For multiple versions CraftChunk is just a wrapper around coordinates (like CraftBlock) without any real information or reference to the chunk. Just create craft chunks in getForceLoadedChunks() with the coordinates without loading them (and they're most probably already loaded anyway), there is a SeverLevel,int,int constructor that you can use instead of the one that takes LevelChunk