Remove nms.Entity#isChunkLoaded

This method was used pre 1.17 era where an Entity was explicitly
tied to a (then called) Chunk's entity slices. If an entity
was not inside a Chunk, then it was considered invalid as
it was not possible to save the entity.

In 1.17+, entities are now tied to a separately tracked entity
section management system. This system is far more reliable now
as it no longer requires a full chunk load to properly track
entities for saving. As a result, an Entity if inside the world
is always attached to some entity chunk section (except in rare
cases in Vanilla which are fixed in Moonrise).

As a result, whether the chunk the entity is in is loaded is no
longer an indication of whether they are tracked in the world
and we can reliably infer that the entity is correctly in the
world through the valid field alone.

Additionally drop the isInWorld() check, as valid=true implies
isInWorld=true. More importantly, the isInWorld() check invokes
getHandle which may trip a thread check on Folia. This will fix
World#getEntities() and friends exploding on Folia.

However, World#getEntities() on Folia still cannot reliably return
all entities in the world as actions such as cross-region
(not cross-world) teleporting will remove entities from the world.

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

@@ -209,8 +209,8 @@ public class CraftWorld extends CraftRegionAccessor implements World {
     @Override
     public int getEntityCount() {
         int ret = 0;
-        for (net.minecraft.world.entity.Entity entity : world.getEntities().getAll()) {
-            if (entity.isChunkLoaded()) {
+        for (net.minecraft.world.entity.Entity entity : this.world.getEntities().getAll()) {
+            if (entity.getBukkitEntity().isValid()) {
                 ++ret;
             }
         }

paper-server/src/main/java/org/bukkit/craftbukkit/entity/CraftEntity.java

@@ -414,7 +414,7 @@ public abstract class CraftEntity implements org.bukkit.entity.Entity {
 
     @Override
     public boolean isValid() {
-        return this.entity.isAlive() && this.entity.valid && this.entity.isChunkLoaded() && this.isInWorld();
+        return this.entity.isAlive() && this.entity.valid;
     }
 
     @Override