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/0421-Add-predicate-for-blocks-when-raytracing.patch

@@ -5,10 +5,10 @@ Subject: [PATCH] Add predicate for blocks when raytracing
 
 
 diff --git a/src/main/java/org/bukkit/World.java b/src/main/java/org/bukkit/World.java
-index f037f46a9c6ce894f24af14c20fb514a58a8aee9..86fd5f3d322b6203f02ca7c427ccd56336b93fc0 100644
+index 24eaf74420f6fbd4f0a0f13b719f57b50696aef3..9a473448427b48038e097796459ff0352f5a54cc 100644
 --- a/src/main/java/org/bukkit/World.java
 +++ b/src/main/java/org/bukkit/World.java
-@@ -1649,6 +1649,27 @@ public interface World extends RegionAccessor, WorldInfo, PluginMessageRecipient
+@@ -1686,6 +1686,27 @@ public interface World extends RegionAccessor, WorldInfo, PluginMessageRecipient
      @Nullable
      public RayTraceResult rayTraceEntities(@NotNull Location start, @NotNull Vector direction, double maxDistance, double raySize, @Nullable Predicate<? super Entity> filter);
  
@@ -36,7 +36,7 @@ index f037f46a9c6ce894f24af14c20fb514a58a8aee9..86fd5f3d322b6203f02ca7c427ccd563
      /**
       * Performs a ray trace that checks for block collisions using the blocks'
       * precise collision shapes.
-@@ -1712,6 +1733,34 @@ public interface World extends RegionAccessor, WorldInfo, PluginMessageRecipient
+@@ -1749,6 +1770,34 @@ public interface World extends RegionAccessor, WorldInfo, PluginMessageRecipient
      @Nullable
      public RayTraceResult rayTraceBlocks(@NotNull Location start, @NotNull Vector direction, double maxDistance, @NotNull FluidCollisionMode fluidCollisionMode, boolean ignorePassableBlocks);
  
@@ -71,7 +71,7 @@ index f037f46a9c6ce894f24af14c20fb514a58a8aee9..86fd5f3d322b6203f02ca7c427ccd563
      /**
       * Performs a ray trace that checks for both block and entity collisions.
       * <p>
-@@ -1745,6 +1794,42 @@ public interface World extends RegionAccessor, WorldInfo, PluginMessageRecipient
+@@ -1782,6 +1831,42 @@ public interface World extends RegionAccessor, WorldInfo, PluginMessageRecipient
      @Nullable
      public RayTraceResult rayTrace(@NotNull Location start, @NotNull Vector direction, double maxDistance, @NotNull FluidCollisionMode fluidCollisionMode, boolean ignorePassableBlocks, double raySize, @Nullable Predicate<? super Entity> filter);