Use specialization constants in clustered renderer

* Keep track of when projector, softshadow or directional sofshadow were enabled.
* Enable them via specializaton constant where it makes sense.
* Re-implements soft shadows.
* Re-implements light projectors.

servers/rendering_server.h

@@ -78,7 +78,8 @@ public:
 		CANVAS_ITEM_Z_MAX = 4096,
 		MAX_GLOW_LEVELS = 7,
 		MAX_CURSORS = 8,
-		MAX_2D_DIRECTIONAL_LIGHTS = 8
+		MAX_2D_DIRECTIONAL_LIGHTS = 8,
+		MAX_MESH_SURFACES = 256
 	};
 
 	/* TEXTURE API */