Fixes missng 2D engine bits

-Mesh2D now works
-MultiMesh2D now works
-Polygon2D now works
-Added hooks for processing 2D particles
-Skeleton2D now works

2D particles still not working, but stuff needed for it is now implemented.

servers/rendering/renderer_rd/renderer_canvas_render_rd.h

@@ -67,12 +67,10 @@ class RendererCanvasRenderRD : public RendererCanvasRender {
 	};
 
 	enum {
-		FLAGS_INSTANCING_STRIDE_MASK = 0xF,
-		FLAGS_INSTANCING_ENABLED = (1 << 4),
-		FLAGS_INSTANCING_HAS_COLORS = (1 << 5),
-		FLAGS_INSTANCING_COLOR_8BIT = (1 << 6),
-		FLAGS_INSTANCING_HAS_CUSTOM_DATA = (1 << 7),
-		FLAGS_INSTANCING_CUSTOM_DATA_8_BIT = (1 << 8),
+
+		FLAGS_INSTANCING_MASK = 0x7F,
+		FLAGS_INSTANCING_HAS_COLORS = (1 << 7),
+		FLAGS_INSTANCING_HAS_CUSTOM_DATA = (1 << 8),
 
 		FLAGS_CLIP_RECT_UV = (1 << 9),
 		FLAGS_TRANSPOSE_RECT = (1 << 10),