Embed modal (#4748)

* Embed modal

* Proxy OEmbed requests from web UI

app/javascript/mastodon/features/ui/util/async-components.js

@@ -109,3 +109,7 @@ export function MediaGallery () {
 export function VideoPlayer () {
   return import(/* webpackChunkName: "status/video_player" */'../../../components/video_player');
 }
+
+export function EmbedModal () {
+  return import(/* webpackChunkName: "modals/embed_modal" */'../components/embed_modal');
+}