Implement more rendering options as specialization constants

* Shadow quality settings now specialization constant.
* Decal and light projector filters can be set.
* Changing those settings forces re-creation of the pipelines.

These changes should help improve performance related to shadow mapping, and allows improving performance by sacrificing decal and light projector quality.

servers/rendering/renderer_scene_cull.h

@@ -1143,6 +1143,9 @@ public:
 
 	PASS1(set_debug_draw_mode, RS::ViewportDebugDraw)
 
+	PASS1(decals_set_filter, RS::DecalFilter)
+	PASS1(light_projectors_set_filter, RS::LightProjectorFilter)
+
 	virtual void update();
 
 	bool free(RID p_rid);