Introduce dimensions.aspectRatio block support

[andrewserong]

In the Gutenberg plugin, an aspect ratio block support feature was added, with support for both Group and Cover blocks. It would be good to backport this feature for the WP 6.5 release.

While the feature is spread across JS and PHP code, it should be possible to land most of the PHP implementation in advance of the JS packages update for core.

The original feature landed in Gutenberg in the following PR: ​https://github.com/WordPress/gutenberg/pull/56897

Backport the aspect ratio block support feature from the Gutenberg plugin, that originally landed in: ​https://github.com/WordPress/gutenberg/pull/56897

Note this PR backports the PHP parts of the block support. This can be safely done prior to the JS packages landing for core, as the UI for the feature will not be exposed until the JS packages are updated.

Testing this PR manually in wordpress-develop is possible via the following steps:

• Update the Group block's block.json file to include dimensions: { aspectRatio: true } under the supports key. I.e. the dimensions support will now look like:

		"dimensions": {
			"aspectRatio": true,
			"minHeight": true
		},

• Skip the block.json cache so the changes to the block.json file are picked up. A quick way is to comment out the following lines:

​https://github.com/WordPress/wordpress-develop/blob/e108d27762f375cab724789c2db1445c4bcd4477/src/wp-includes/blocks.php#L346-L348

• In a post or page add the following markup that contains a Group block with an aspect-ratio set:

<div class="wp-block-group has-background" style="background-color:#f0d1d1">
<p>A group block</p>
</div>

• Note: at this stage you won't yet see the aspect ratio rendered in the editor — this is to be expected as JS rendering will only happen once the JS packages are updated.
• Save the post or page and load the post on the site frontend. You should see that the aspect ratio rules are output for this block, along with a min-height:unset rule:

Trac ticket: https://core.trac.wordpress.org/ticket/60365

[isabel_brison]

In 57491:

Editor: introduce dimensions.aspectRatio block support.

Adds front end rendering logic for the dimensions.aspectRatio block support as well as the required logic in WP_Theme_JSON and the style engine.

Props andrewserong.
Fixes #60365.

Committed in r57491.

Wonderful, thank you @tellthemachines! 🙇