[RNMobile] Add registration of new block for native mobile

[guarani]

Description

Registers a new block for native mobile.

How has this been tested?

See wordpress-mobile/gutenberg-mobile#4291.

Types of changes

• New feature

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• I've tested my changes with keyboard and screen readers.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR (please manually search all *.native.js files for terms that need renaming or removal).

[SiobhyB]

Verified that this contains all the changes needed to add a new block, release notes aren't necessary as the block isn't a core one and will initially only be available on development builds

[guarani]

Thanks @SiobhyB!