Add 2D shadows and canvas SDF to OpenGL3 renderer

This is an initial implementation based on the current RD implementation

Performance will improve later

servers/rendering/dummy/rasterizer_canvas_dummy.h

@@ -39,7 +39,6 @@ public:
 	void free_polygon(PolygonID p_polygon) override {}
 
 	void canvas_render_items(RID p_to_render_target, Item *p_item_list, const Color &p_modulate, Light *p_light_list, Light *p_directional_list, const Transform2D &p_canvas_transform, RS::CanvasItemTextureFilter p_default_filter, RS::CanvasItemTextureRepeat p_default_repeat, bool p_snap_2d_vertices_to_pixel, bool &r_sdf_used) override {}
-	void canvas_debug_viewport_shadows(Light *p_lights_with_shadow) override {}
 
 	RID light_create() override { return RID(); }
 	void light_set_texture(RID p_rid, RID p_texture) override {}