Lock widget room ID when added

This changes the widget room ID available to widget URL templates so that it's
locked to the room the widget was added in.

Fixes https://github.com/vector-im/element-web/issues/16337

src/stores/widgets/StopGapWidget.ts

@@ -190,7 +190,7 @@ export class StopGapWidget extends EventEmitter {
 
     private runUrlTemplate(opts = {asPopout: false}): string {
         const templated = this.mockWidget.getCompleteUrl({
-            currentRoomId: RoomViewStore.getRoomId(),
+            widgetRoomId: this.roomId,
             currentUserId: MatrixClientPeg.get().getUserId(),
             userDisplayName: OwnProfileStore.instance.displayName,
             userHttpAvatarUrl: OwnProfileStore.instance.getHttpAvatarUrl(),