Add AMP compatibility for OpenTable block

[westonruter]

See #14395

This fixes AMP compatibility for the OpenTable block by rendering an amp-iframe as opposed to the embed script on AMP pages. Note that the block edit function similarly constructs and iframe for preview purposes, so manually constructing the iframe is not unprecedented.

👉 Note this is currently blocked by an AMP bug which has been fixed upstream but is not yet in production. See ampproject/amphtml#29398. In order to test this PR, you need to first opt-in to to the beta-channel on the AMP Experiments page. The fix should be rolled out to AMP's production channel by September 22nd. The fix is now live.

Given this HTML content:

<!-- wp:jetpack/opentable {"rid":["150220"]} -->
<div class="wp-block-jetpack-opentable"><a href="https://www.opentable.com/restref/client/?rid=150220">https://www.opentable.com/restref/client/?rid=150220</a></div>
<!-- /wp:jetpack/opentable -->

<!-- wp:jetpack/opentable {"rid":["150220"],"style":"tall","className":"is-style-tall"} -->
<div class="wp-block-jetpack-opentable is-style-tall"><a href="https://www.opentable.com/restref/client/?rid=150220">https://www.opentable.com/restref/client/?rid=150220</a></div>
<!-- /wp:jetpack/opentable -->

<!-- wp:jetpack/opentable {"rid":["150220"],"style":"wide","align":"wide","className":"is-style-wide"} -->
<div class="wp-block-jetpack-opentable alignwide is-style-wide"><a href="https://www.opentable.com/restref/client/?rid=150220">https://www.opentable.com/restref/client/?rid=150220</a></div>
<!-- /wp:jetpack/opentable -->

<!-- wp:jetpack/opentable {"rid":["150220"],"style":"button","align":"","className":"is-style-button"} -->
<div class="wp-block-jetpack-opentable is-style-button"><a href="https://www.opentable.com/restref/client/?rid=150220">https://www.opentable.com/restref/client/?rid=150220</a></div>
<!-- /wp:jetpack/opentable -->

<!-- wp:paragraph -->
<p>Multi:</p>
<!-- /wp:paragraph -->

<!-- wp:jetpack/opentable {"rid":["150220","1076311"]} -->
<div class="wp-block-jetpack-opentable"><a href="https://www.opentable.com/restref/client/?rid=150220">https://www.opentable.com/restref/client/?rid=150220</a><a href="https://www.opentable.com/restref/client/?rid=1076311">https://www.opentable.com/restref/client/?rid=1076311</a></div>
<!-- /wp:jetpack/opentable -->

Non-AMP	AMP Before 👎	AMP After 👍

Changes proposed in this Pull Request:

• Add AMP compatibility for OpenTable block by using amp-iframe on AMP pages as opposed to OpenTable embed script.

Jetpack product discussion

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

Testing instructions:

• Create a post with OpenTable blocks
• Compare non-AMP and AMP
• The two should be identical

Proposed changelog entry for your changes:

• Add AMP compatibility for OpenTable block

[jetpackbot]

Scheduled Jetpack release: October 6, 2020.
Scheduled code freeze: September 29, 2020

E2E results is available here (for debugging purposes): https://jetpack-e2e-dashboard.herokuapp.com/pr-17085

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 1652d91

[westonruter]

@jeherve No longer [Status] Blocked / Hold.

[jeherve]

Internal reference: D50129-code