[TEST][DO NOT MERGE][Gutenberg] Embed block: Implement specific Embed preview

[fluiddot]

Enables the embed block inline preview to be tested with an installable build.

NOTE: ⚠️ This PR was created for testing purposes only so it shouldn't be merged.

Regression Notes

1. Potential unintended areas of impact
   N/A

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

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

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

[peril-wordpress-mobile]

You can test the changes on this Pull Request by downloading it from AppCenter here with build number: 54634. IPA is available here. If you need access to this, you can ask a maintainer to add you.

[peril-wordpress-mobile]

	Warnings
⚠️	This PR is tagged with 'DO NOT MERGE'.

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