External Media: Enable for Cover block

[obenland]

Enables External Media feature for the Cover block.

Changes proposed in this Pull Request:

• Adds core/cover to the list of blocks External Media is available to.

Does this pull request change what data or activity we track or use?

No

Testing instructions:

• In the Editor, insert a Cover block and chose an External Media provider to insert a background image.
• Replace the image with a different one.

Proposed changelog entry for your changes:

• Makes External Media available to the Cover block.

[matticbot]

Caution: This PR has changes that must be merged to WordPress.com
Hello obenland! These changes need to be synced to WordPress.com - If you 're an a11n, please commandeer and confirm D50959-code works as expected before merging this PR. Once this PR is merged, please commit the changes to WP.com. Thank you!
This revision will be updated with each commit to this PR

[obenland]

@marekhrabe @retrofox Do you remember why we initially decided to not make External Media available to the Cover block?

[jetpackbot]

Scheduled Jetpack release: November 3, 2020.
Scheduled code freeze: October 27, 2020

E2E results is available here (for debugging purposes): https://jetpack-e2e-dashboard.herokuapp.com/pr-17441

Thank you for the great PR description!

When this PR is ready for review, please apply the [Status] Needs Review label. If you are an a11n, please have someone from your team review the code if possible. The Jetpack team will also review this PR and merge it to be included in the next Jetpack release.

Generated by 🚫 dangerJS against 53c834e

[retrofox]

@marekhrabe @retrofox Do you remember why we initially decided to not make External Media available to the Cover block?

Was no valid reason, AFAIK. I presume it was just a way to extend the media button progressively to other blocks. Add it to cover makes total sense to me.

[retrofox]

LGTM

[obenland]

r215148-wpcom