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

[aaronrobertshaw]

This ticket tracks the backporting of PHP files for the following Gutenberg changes:

​https://github.com/WordPress/gutenberg/pull/61033

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

Syncs the changes from:

• ​https://github.com/WordPress/gutenberg/pull/61033

These changes ensure that custom feature-level selectors for style nodes are correctly scoped when generating a theme.json stylesheet

Unit tests: npm run test:php -- --filter Tests_Theme_wpThemeJson

Trac ticket: https://core.trac.wordpress.org/ticket/61119

👋 @audrasjb @aaronrobertshaw any updates here?

All the feedback to date has been addressed and we're just waiting on an approval.

[isabel_brison]

In 58244:

Editor: Add scoping of feature level global styles selectors.

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

Props aaronrobertshaw, audrasjb, vcanales, isabel_brison.
Fixes #61119.

Committed in r58244.

[kebbet]

Please milestone in 6.6 @isabel_brison

[isabel_brison]

Oh sorry @kebbet, didn't notice the ticket wasn't milestoned already!