Initial Port of Jetpack Tiled Gallery Block

[SiobhyB]

Fixes wordpress-mobile/gutenberg-mobile#4268

This PR brings the first iteration of the Tiled Gallery block to the iOS app.

To test: Please refer to the Jetpack PR as the "central PR" with the most up-to-date testing instructions.

Related PRs

• Jetpack: [RNMobile] Initial Port of Jetpack Tiled Gallery Block Automattic/jetpack#21849
• Gutenberg Mobile: Initial Port of Jetpack Tiled Gallery Block gutenberg-mobile#4291
• Android: Initial Port of Jetpack Tiled Gallery Block WordPress-Android#15619
• Gutenberg: [RNMobile] Add registration of new block for native mobile WordPress/gutenberg#37776

Regression Notes

1. Potential unintended areas of impact

This PR adds a new block, and it is only available on development builds, so there is little potential impact on other parts of the app.

2. What I did to test those areas of impact (or what existing automated tests I relied on)

We just relied on existing Gutenberg Mobile and WPiOS tests.

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

We added a test in wordpress-mobile/gutenberg-mobile#3903 but wordpress-mobile/gutenberg-mobile#4168 needs to be resolved before we can add more tests.

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 trigger an installable build for these changes by visiting CircleCI here.

[peril-wordpress-mobile]

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

[guarani]

I tested this change by loading the Square layout and things are working as expected, so I'm approving this now.

I added the DO NOT merge label because:

• The linked Jetpack PR needs to be merged first
• Then the Gutenberg Mobile PR (and Gutenberg PR) need to be merged and a tagged release created

I also added the next milestone since we hope to get this merged soon. I also intentionally did not add release notes, since this block will only be available when connecting to the Metro server running out of the Gutenberg Mobile repo.