Add UI tests to unsupported block editor

[guarani]

Addresses: #2358

Adds UI tests to the unsupported block editor.

Test that tapping on the help button of an unsupported block shows the bottom sheet. Tapping on the edit button in the bottom sheet shows the unsupported block web view editor.

Android	iOS

To test:

1. Ensure tests are green (if running locally, run yarn test:e2e:ios:local __device-tests__/gutenberg-editor-unsupported-blocks.test.js)
2. Optional: Ensure the test catches a failure to open the web view; comment out these lines and ensure the tests fail: https://github.com/WordPress/gutenberg/pull/21150/files#diff-48d07c563702293f97bb8137c7ad9057R115-R119

PR submission checklist:

• I have considered adding unit tests where possible.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[peril-wordpress-mobile]

Wanna run full suite of Android and iOS UI tests? Click here and 'Approve' CI job!

[guarani]

I figured out why this PR fails when running locally, when it wasn't before.

First of all, I remembered CircleCI now only runs canary tests by default—so CircleCI actually isn't running the tests I added in this PR (unless I manually run them from the peril comment above).

As mentioned at the bottom of __device-tests__/README.md, the __DEV__ flag is false for UI tests because the packager is not used; the app is bundled an that is used.

When I started this PR, its branch was based off #2063 (and WordPress/gutenberg#21150) at a time when the unsupported blocks UI was not behind a __DEV__ flag. So these UI tests worked up until we put things behind the __DEV__ flag.

Now the question is, how to run UI tests on a feature that's behind a __DEV__ flag?

[guarani]

I found a fix using for iOS:

yarn ios --configuration Release && TEST_RN_PLATFORM=ios yarn device-tests:local __device-tests__/gutenberg-editor-unsupported-blocks.test.js

and Android

yarn android && TEST_RN_PLATFORM=android yarn device-tests:local __device-tests__/gutenberg-editor-unsupported-blocks.test.js

I don't know if there's a better solution. Otherwise, this is ready for testing again @etoledom and @marecar3.

[guarani]

Closing in favor of WordPress/gutenberg#23729. Since the monorepo has been merged, UI test code now belongs in the Gutenberg repo.