Project issue: Unsupported blocks fallback mechanism

[guarani]

Description

Implement a fallback mechanism for unsupported blocks. A user who encounters an unsupported blocks should be able to view and edit the block in question, without leaving the mobile Gutenberg editor.

Required to ship to the public:

• Enable unsupported block editing on dev builds
  • Gutenberg PR
  • Gutenberg Mobile PR
  • WPAndroid PR
  • WPiOS PR
  • UI tests PR UI tests PR
• Fix support for Atomic sites
• Move resources to /rn-gutenberg-bridge(discussion).
• Test with the monorepo branch
  • Investigate reports of a "welcome to your site” screen shown while trying to edit an unsupported block (reported on Android)
• Add basic usage track events
• Fix the \n issue
• Add test cases to manual test suite
• Enable unsupported block editing on all builds

Extras:

• Fix Auth issues after login
• Handle the case when Gutenberg is disabled/unavailable on the backend (iOS, Android)
• Unsupported Block Editor not working on sites where Jetpack is connected to WordPress.com
• Increase tap-target of primary action on unsupported blocks Increase tap-target of primary action on unsupported blocks #2567
• Unsupported block bottom sheet is triggered when device is rotated

To Dos:

• Enable the Unsupported Block Editor on Jetpack/Atomic sites where the Classic editor is the default
• Enable the Unsupported Block Editor on posts from self-hosted sites
• Improve the Unsupported Block Editor offline experience
• Make fallback option more discoverable (cog icon on block toolbar with options) cc @iamthomasbishop .
• Try fix WebView title for 3rd party blocks.
• Bottom sheet separators should go from side to side.
• (Android-only) Investigate report of keyboard popping up unexpectedly

Additional infomation

• Early discussion about project: Fallback to browser for unsupported blocks #1488

[etoledom]

We are finishing the focus on this feature after merging the main PRs (WordPress/gutenberg#21150 WordPress/gutenberg#25238) and the most important side PRs described on this ticket.

What's left will be worked later on after new assignments are made.