Global Styles: Add scoping of feature level selectors for custom block style variations

[aaronrobertshaw]

Related:

• Block Styles: Extend block style variations as mechanism for achieving section styling #57908

Note: The changes in this PR are being split out from #57908 to make that more manageable

What?

Ensures that feature-level selectors for block style variations are correctly scoped when generating a theme.json stylesheet.

Important: Currently, only block styles registered via block.json on core blocks are supported through theme.json. This means the supported blocks and their block styles don't currently leverage feature-level selectors. The issue this PR addresses would only surface once custom block style variations can be defined via theme.json in #57908.

Why?

To ensure that once custom block style variations being registered via theme.json are supported, the resulting CSS selectors are correct.

Testing Instructions

• There should be no change to existing core block style variations that can be styled via Global Styles e.g. Image rounded
• npm run test:unit:php:base -- --filter WP_Theme_JSON_Gutenberg_Test

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Co-authored-by: aaronrobertshaw <aaronrobertshaw@git.wordpress.org>
Co-authored-by: talldan <talldanwp@git.wordpress.org>

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[talldan]

Guessing this one will need a PHP backport, so I've added the label.

[talldan]

Thanks for adding the test. I don't see any issues here, though I'm not particularly familiar with this part of the codebase, so if you want a second approval it might not be a bad idea.

[aaronrobertshaw]

Thanks for the reviews @talldan 🙇

so if you want a second approval it might not be a bad idea.

I'm pretty comfortable with this one.

The scoping of node selectors in this class was added separately to the selectors API but around the same time. This PR just makes it work as expected and correctly scope any custom selectors defined by the block via the selectors API.

The underlying issue hasn't surfaced previously as the few use cases that would scope things never needed custom selectors to target inner block markup. That will change with the extended block style variations feature.

[aaronrobertshaw]

Backport for the PHP changes here can be found in WordPress/wordpress-develop#6475