Reusable blocks can't be edited through UBE

[fluiddot]

Describe the bug
Due to recent changes in the editing flow on the web version, editing Reusable blocks through UBE is not working.

The main change is that saving the content is now done in the publish process so there's no longer the Edit/Save buttons in the block UI to apply the changes as we had previously.

New editing flow - Web version

reusable-block-editing-new-flow-web.mp4

To Reproduce
Since in development mode Reusable blocks are rendered, there're two ways to reproduce it.

Development mode (block content rendered)

Steps

1. Go to a post that has some Reusable blocks included the content.
2. Tap twice on a Reusable block.
3. Tap on Edit using web editor.
4. Modify the content of the block.
5. Tap on Continue or ✔️ button to apply the changes.
6. Check that the content is not being modified.

Production mode (block content rendered as a Missing block)

Steps

1. Go to a post that has some Reusable blocks included the content.
2. Tap twice on a Reusable block.
3. Tap on Edit using web editor.
4. Modify the content of the block.
5. Tap on Continue or ✔️ button to apply the changes.
6. Since the content is not rendered in production try to edit the block again.
7. Check that the content is not being modified.

Expected behavior
Reusable block content should be editable through UBE.

Screenshots

reusable-block-ube.mp4

Smartphone (please complete the following information):

• Device: Pixel 4 (emulator)
• OS: Android 11
• Version alpha-269

Additional context
No.

[fluiddot]

Addressed via #3067.