Redirect widgets to another location before deleting them

This is so that shutdown hooks in the widget can correctly fire, such as Jitsi's hook to abandon its hold on the webcam.

Fixes https://github.com/vector-im/riot-web/issues/7351

src/components/views/elements/AppTile.js

@@ -318,6 +318,19 @@ export default class AppTile extends React.Component {
                         }
                         this.setState({deleting: true});
 
+                        // HACK: This is a really dirty way to ensure that Jitsi cleans up
+                        // its hold on the webcam. Without this, the widget holds a media
+                        // stream open, even after death. See https://github.com/vector-im/riot-web/issues/7351
+                        if (this.refs.appFrame) {
+                            // In practice we could just do `+= ''` to trick the browser
+                            // into thinking the URL changed, however I can foresee this
+                            // being optimized out by a browser. Instead, we'll just point
+                            // the iframe at a page that is reasonably safe to use in the
+                            // event the iframe doesn't wink away.
+                            // This is relative to where the Riot instance is located.
+                            this.refs.appFrame.src = '/config.json';
+                        }
+
                         WidgetUtils.setRoomWidget(
                             this.props.room.roomId,
                             this.props.id,