See #14395

Given this post_content:

<!-- wp:separator -->
<hr class="wp-block-separator"/>
<!-- /wp:separator -->

<!-- wp:jetpack/google-calendar {"url":"https://calendar.google.com/calendar/embed?src=askenergy%40oregon.gov\u0026ctz=America/Los_Angeles"} -->
<a href="https://calendar.google.com/calendar/embed?src=askenergy%40oregon.gov&amp;ctz=America/Los_Angeles" class="wp-block-jetpack-google-calendar">https://calendar.google.com/calendar/embed?src=askenergy%40oregon.gov&amp;ctz=America/Los_Angeles</a>
<!-- /wp:jetpack/google-calendar -->

<!-- wp:separator -->
<hr class="wp-block-separator"/>
<!-- /wp:separator -->

Google Calendar is currently not rendering at all on an AMP page. This is because it is getting removed due to not having a width defined on the amp-iframe:

This PR fixes that issue by supplying the proper layout of fixed-height rather than responsive, since the width is intended to be 100%. (This appears to be a regression introduced in #14835.) Also missing in the previous implementation was the placeholder child which is required for amp-iframe elements appearing in the initial viewport. So a link to the Google Calendar was supplied as a placeholder in this case.

This PR also goes beyond just fixing AMP compatibility in that the page is actually better than the non-AMP version when JS is turned off, by supplying a the plain HTML calendar view to visitors with JS turned off. Some additional AMP-specific CSS was included here, but that will eventually not be needed once those are accounted for in AMP itself. See ampproject/amphtml#29846.

Before

Non-AMP w/ JS	Non-AMP w/o JS	AMP 👎	AMP w/o JS 👎
		(Removed by plugin sanitizer)	(Removed by plugin sanitizer)

After

Non-AMP w/ JS	Non-AMP w/o JS	AMP 👍	AMP w/o JS 👍
(No change)	(No change)		(No-JS fallback!)

Changes proposed in this Pull Request:

• Fix AMP compatibility in Google Calendar block.

Jetpack product discussion

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

Testing instructions:

1. Copy the above post_content into a new post.
2. Activate the AMP plugin and enable Transitional mode.
3. Compare the post in AMP and non-AMP (e.g. via Paired Browsing).

Proposed changelog entry for your changes:

• Fix AMP compatibility in Google Calendar block.