revert the removal of MwLLBeginDraw/EndDraw, turns out the newer system still doesn't please weston and likely other compositors

src/backend/cocoa.m

@@ -1001,6 +1001,14 @@ static void MwLLDestroyImpl(MwLL handle) {
 	free(handle);
 }
 
+static void MwLLBeginDrawImpl(MwLL handle) {
+	(void)handle;
+}
+
+static void MwLLEndDrawImpl(MwLL handle) {
+	(void)handle;
+}
+
 static void MwLLPolygonImpl(MwLL handle, MwPoint* points, int points_count,
 			    MwLLColor color) {
 	MilskoCocoa* h = handle->cocoa.real;