Mailchimp Block: Replace submit button with inner button block

[aaronrobertshaw]

Fixes #15712

Changes proposed in this Pull Request:

• Replace the SubmitButton in the Mailchimp block with new shared Button block.

Is this a new feature or does it add/remove features to an existing part of Jetpack?

• No.

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

• No.

Prerequisites:

• Mailchimp account
• Site with Mailchimp connection setup
• Post with Mailchimp block created prior to applying this PR's changes

Testing instructions:

1. Apply this PR
2. On the frontend, visit the post containing the previous version of Mailchimp block
3. Confirm that the block displays and functions as it did before
4. Edit the post
5. Confirm Mailchimp block displays and has correct settings
6. Update the Mailchimp block's button using new settings controls provided by button block
7. Save the post
8. Re-visit the post on the frontend and confirm display and function of block.

Before:

After:

Proposed changelog entry for your changes:

• Update Mailchimp block to use new shared Button block.

[jetpackbot]

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.

E2E results is available here (for debugging purposes): https://jetpack-e2e-dashboard.herokuapp.com/pr-16170

Scheduled Jetpack release: July 7, 2020.
Scheduled code freeze: June 30, 2020

Generated by 🚫 dangerJS against 3534168

[fgiannar]

Other than the PHPCS rule comment above, everything looks good, thanks!

Change already committed

[matticbot]

Caution: This PR has changes that must be merged to WordPress.com
Hello aaronrobertshaw! These changes need to be synced to WordPress.com - If you 're an a11n, please commandeer, review, and approve D45260-code before merging this PR. Thank you!
This revision will be updated with each commit to this PR

[jeherve]

r210103-wpcom