[Impeller] Present Impeller contents in a transaction when there is a platform view (flutter#37809)

Author: zanderso

shell/platform/darwin/ios/ios_surface_metal_impeller.mm

@@ -48,6 +48,12 @@
   if (!CGSizeEqualToSize(drawable_size, layer.drawableSize)) {
     layer.drawableSize = drawable_size;
   }
+
+  // When there are platform views in the scene, the drawable needs to be presented in the same
+  // transaction as the one created for platform views. When the drawable are being presented from
+  // the raster thread, there is no such transaction.
+  layer.presentsWithTransaction = [[NSThread currentThread] isMainThread];
+
   return layer;
 }