Render presets coming from the settings of a section

[oandregal]

What?

This PR renders the presets coming from a section (a block instance). Follow-up to #40547 (depends on it).

Why?

We want to create the concept of a "section" that is able hold settings & styles (like theme.json does) but in block instances. See #40318 and #39281

We need the ability for the presets defined in this sections to be rendered.

How?

This adds the settings as a block support in the server.

Testing Instructions

• Create a new post and open the code editor.
• Paste the following content:

<!-- wp:group {"settings":{"color":{"defaultPalette":false,"palette":{"custom":[{"slug":"my-hotpink","color":"hotpink","name":"Hotpink"}]}}}} -->
<div class="wp-block-group"><!-- wp:paragraph -->
<p>Leaf paragraph of top-level group block.</p>
<!-- /wp:paragraph -->

<!-- wp:group {"settings":{"color":{"palette":{"custom":[{"slug":"my-aquamarine","color":"aquamarine","name":"Aquamarine"}]}}}} -->
<div class="wp-block-group"><!-- wp:paragraph -->
<p>Leaf paragraph of inner group block.</p>
<!-- /wp:paragraph --></div>
<!-- /wp:group --></div>
<!-- /wp:group -->

• Go to the front and verify that there's a new inline styles with the following contents:

body {--wp--preset--color--my-hotpink: hotpink; }
.has-my-hotpink-color { color: var(--wp--preset--color--my-hotpink) !important; }
.has-my-hotpink-background-color { background-color: var(--wp--preset--color--my-hotpink) !important; }
.has-my-hotpink-border-color { border-color: var(--wp--preset--color--my-hotpink) !important; }

TODO

This PR is in bootstrap state. It needs to be updated for the styles generated to be in line with this conversation #40547 (comment)

[oandregal]

This needs more work than anticipated and I won't be able to take it. Closing this draft as to invite others to start from a blank slate.