Quote blocks: add background image and minimum height support

[ramonjd]

What?

This PR adds support for background images for the Pullquote and Quote blocks.

For flexibility to display varying image heights, it also opts in to minimum height for these blocks, but not as a default control.

Why?

The blockquote element has indentation — an inherit visual property that serves to differentiate it from surrounding text.

The ability to add background images extends visual differentiation, and allows users to set unique design patterns. Example:

As for adding minimum height support, it ensures that users can adequately space quote blocks to accommodate taller images.

How?

Turning on the block supports in block.json

Testing Instructions

Add a Quote and Pullquote block to a post.

Select background images for both, and play around with minimum height and other styles according to your delight.

Here's some HTML to get you started:

<!-- wp:quote -->
<blockquote class="wp-block-quote"><!-- wp:paragraph -->
<p>"I love mountains..."</p>
<!-- /wp:paragraph --></blockquote>
<!-- /wp:quote -->

<!-- wp:pullquote -->
<figure class="wp-block-pullquote"><blockquote><p>"And forests!"</p><cite>Me</cite></blockquote></figure>
<!-- /wp:pullquote -->

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Co-authored-by: ramonjd <ramonopoly@git.wordpress.org>
Co-authored-by: tellthemachines <isabel_brison@git.wordpress.org>

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[ramonjd]

Should we collapse the background image tools panel by default?

I'm tending towards "yes" - there are quite a few controls here.

[ramonjd]

Ignore this. It's pretty compact

[tellthemachines]

Yeah it doesn't bother me! Also helps with discoverability.

[tellthemachines]

Nice! This is a useful enhancement and works well in testing ✅

[ramonjd]

Thanks for the lightning fast reviews 🙇🏻