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/api/0455-More-Raid-API.patch

@@ -39,10 +39,10 @@ index 983a8c20a06d2b509602b27f49c090598b8ecc42..fa98599e3eee37bf68f0e9813497c718
 +    // Paper end
  }
 diff --git a/src/main/java/org/bukkit/World.java b/src/main/java/org/bukkit/World.java
-index 16570c3c7ed5e7ad25f20c1034f7b966d6e694da..adcd8161846b06fd1a7895750f98b629204a8406 100644
+index ba57efc267e78d28c67648b0e994ffca3b8a8823..bb70a797ea5f0db5bd9f2397944687530b0d1cf3 100644
 --- a/src/main/java/org/bukkit/World.java
 +++ b/src/main/java/org/bukkit/World.java
-@@ -4127,6 +4127,17 @@ public interface World extends RegionAccessor, WorldInfo, PluginMessageRecipient
+@@ -4164,6 +4164,17 @@ public interface World extends RegionAccessor, WorldInfo, PluginMessageRecipient
      @Nullable
      public Raid locateNearestRaid(@NotNull Location location, int radius);