Video Block: empty placeholder remains when replacing deleted video

#### Steps to reproduce the issue

1. Start with a site that's connected to WordPress.com, and where the Video feature is enabled under Jetpack > Settings > Performance
2. Go to Posts > Add New
3. Add a new video block, upload a video, publish your post.
4. Go to the Media library, and delete the video you've just added.
5. Go back to the post editor, you should see a placeholder instead of the now deleted video.
6. Click on Replace in the block tools, and upload a new video.
7. Once the upload is complete, you won't see its preview in the editor until you refresh the page.

Original report: p8oabR-DS-p2#comment-5180
Related: #19271 cc @stacimc

Start in the WordPress post editor with the Video block and reproduce the replacement flow described: delete the original video, then replace it after uploading a new one. Trace the block's preview update after upload and confirm that the new video preview appears without a page refresh.

Written by the indexing model from the issue text.