Add Shader compile groups to RD Shader system

This allows us to specify a subset of variants to compile at load time and conditionally other variants later.

This works seamlessly with shader caching.

Needed to ensure that users only pay the cost for variants they use

servers/rendering/renderer_rd/pipeline_cache_rd.h

@@ -91,7 +91,11 @@ public:
 		return result;
 	}
 
-	_FORCE_INLINE_ uint32_t get_vertex_input_mask() const {
+	_FORCE_INLINE_ uint32_t get_vertex_input_mask() {
+		if (input_mask == 0) {
+			ERR_FAIL_COND_V(shader.is_null(), 0);
+			input_mask = RD::get_singleton()->shader_get_vertex_input_attribute_mask(shader);
+		}
 		return input_mask;
 	}
 	void clear();