SPIGOT-6729: Add Chunk.isEntitiesLoaded()

By: Brokkonaut <hannos17@gmx.de>

paper-server/src/main/java/org/bukkit/craftbukkit/CraftChunk.java

@@ -111,6 +111,11 @@ public class CraftChunk implements Chunk {
         return new CraftBlock(worldServer, new BlockPosition((this.x << 4) | x, y, (this.z << 4) | z));
     }
 
+    @Override
+    public boolean isEntitiesLoaded() {
+        return getCraftWorld().getHandle().entityManager.a(ChunkCoordIntPair.pair(x, z)); // PAIL rename isEntitiesLoaded
+    }
+
     @Override
     public Entity[] getEntities() {
         if (!isLoaded()) {