Update synced media references when saving a post with ongoing uploads

[fluiddot]

Fixes WordPress/gutenberg#33593

To test:

1. Create a post.
2. Add a gallery block and tap "Add Media".
3. Select "Choose from device" option.
4. Select multiple images from the device and confirm the selection.
5. While images are uploading, leave the editor.
6. Wait for uploads to complete while in the post list.
7. Re-open the post with the gallery block.
8. Tap on the post settings button (three dots button located at the top).
9. Tap on "Switch to HTML mode"
10. Observe that the src attributes of all img tags reference a remote URL and not a local version.
    • Remote URLs start with https://
    • Local URLs start with ///

Regression Notes

1. Potential unintended areas of impact
   The fix is specific to the post save process when there are uploads in progress, so apart from this area, I don't expect other unintended areas of impact.

2. What I did to test those areas of impact (or what existing automated tests I relied on)
   I tested in the following scenarios for this area:

• Save a post with completed and pending media uploads
• Save a post with only pending media uploads
• Save a post with no media uploads

3. What automated tests I added (or what prevented me from doing so)
   N/A

PR submission checklist:

• I have completed the Regression Notes.
• I have considered adding unit tests for my changes.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[peril-wordpress-mobile]

You can test the changes on this Pull Request by downloading it from AppCenter here with build number: 56815. IPA is available here. If you need access to this, you can ask a maintainer to add you.

[peril-wordpress-mobile]

You can trigger optional UI/connected tests for these changes by visiting CircleCI here.

[mokagio]

I'm going to bump this to the next release because we'll be code freezing 18.4 today and this hasn't been approved yet.

If this cannot wait two weeks and it's important that it makes it into this release, let me know and we'll organize a new beta once ready.

[fluiddot]

I'm going to bump this to the next release because we'll be code freezing 18.4 today and this hasn't been approved yet.

If this cannot wait two weeks and it's important that it makes it into this release, let me know and we'll organize a new beta once ready.

Thanks @mokagio for bumping it to the next release 🙇 , this fix is not critical so it can wait to the next version.

[ceyhun]

I was able to reproduce the issue consistently following the instructions in WordPress/gutenberg#33593 (comment) and verified the fix and it LGTM 👍 We only need to update the release notes to be in the correct version.

[fluiddot]

I was able to reproduce the issue consistently following the instructions in WordPress/gutenberg#33593 (comment) and verified the fix and it LGTM 👍 We only need to update the release notes to be in the correct version.

Thanks @ceyhun for the review ❤️! I've just updated the release notes in this commit, once the CI checks pass I'll merge it.