Implements procedural ground tile generation

Adds procedural ground tile generation with chunking for improved performance.

Includes:
- Ground tile entity with debug text and cell information
- Grass and tree placement based on cell data
- Ground shader for visual representation
- Chunk loading and unloading system based on player position

Entities/GroundTile/scripts/grass_multimesh.gd.uid

@@ -0,0 +1 @@
+uid://btju6b83mvgvk