Implement SmartFrame embedding

[alshakero]

Changes proposed in this Pull Request:

This PR adds support for SmartFrame embedding. It's heavily inspired by (more like shamelessly copies) gettyimages embedding logic. It adds support for:

1. It adds a SmartFrame embedding block, you can test it by adding a "SmartFrame" block and use this URL to test.
2. Smartframe URLs URLs using the embed block.
3. SmartFrame shortcodes like [jetpack_smartframe script-id="6ae67829d1264ee0ea6071a788940eae" image-id="mantymetsa_1630927773870" width="100%" max-width="1412px"].
4. SmartFrame embed code, it transforms it into a safe shortcode.

<script src="https://embed.smartframe.io/6ae67829d1264ee0ea6071a788940eae.js" data-image-id="mantymetsa_1630927773870" data-width="100%" data-max-width="1412px"></script>

Fixes #21062

Jetpack product discussion

Context here: p58i-b8R-p2

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

No

Testing instructions:

1. Apply D66901-code diff on your sandbox.
2. Sandbox a site. Create a new post.
3. Using the SmartFrame component, embed https://mikael-korpela.smartframe.io/p/mantymetsa_1630927773870/7673dc41a775fb845cc26acf24f1fe4f (you can add random query params to verify the regex catches any valid URL).
4. Using the embed component, embed https://mikael-korpela.smartframe.io/p/mantymetsa_1630927773870/7673dc41a775fb845cc26acf24f1fe4f (you can add random query params to verify the regex catches any valid URL).
5. Using the shortcode component, please test [jetpack_smartframe script-id="6ae67829d1264ee0ea6071a788940eae" image-id="mantymetsa_1630927773870" width="100%" max-width="1412px"]. Only script-id and image-id are required, and the embed should work without the rest.
6. Using custom HTML block, use the embed code they provide <script src="https://embed.smartframe.io/6ae67829d1264ee0ea6071a788940eae.js" data-image-id="mantymetsa_1630927773870" data-width="100%" data-max-width="1412px"></script>

[matticbot]

Caution: This PR has changes that must be merged to WordPress.com
Hello alshakero! These changes need to be synced to WordPress.com - If you 're an a11n, please commandeer and confirm D66901-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

[github-actions]

Thank you for your PR!

When contributing to Jetpack, we have a few suggestions that can help us test and review your patch:

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Jetpack plugin:

• Next scheduled release: October 5, 2021.
• Scheduled code freeze: September 28, 2021.

[jeherve]

Thanks for the PR! I gave it a first pass below.

[alshakero]

@jeherve Your feedback really shaped the PHP code up! Thank you so much. Addressed all.

[jeherve]

Is this ready for another review now?

[alshakero]

@jeherve Yes! Forgot to change the labels.

[jeherve]

This tests well for me. 🚢

[jeherve]

approving again after our discussion in p1632232389218000-slack-CBG1CP4EN

[github-actions]

Great news! One last step: head over to your WordPress.com diff, D66901-code, and commit it.
Once you've done so, come back to this PR and add a comment with your changeset ID.

Thank you!

[alshakero]

r232103-wpcom