Editor: Reuse the shared selector-list parser in the states block support

[itzmekhokan]

wp_split_selector_list() in the states block support (src/wp-includes/block-supports/states.php, added in [62453] / #65239) splits a CSS selector list on top-level commas but only tracks parenthesis depth. It therefore mis-splits selectors that contain commas inside strings, escaped commas, or CSS comments:

Input	Before	Correct
[data-label="Save, continue"]	['[data-label="Save', ' continue"]']	one selector
.foo\,bar,.baz	['.foo\', 'bar', '.baz']	['.foo\,bar', '.baz']

In the same release, [62607] / #65265 added WP_Theme_JSON::split_selector_list(), a robust parser that already handles commas inside strings, escaped commas, CSS comments, and CDO/CDC tokens — the exact cases the states copy gets wrong.

Changes

• Make WP_Theme_JSON::split_selector_list() public (was protected). The class is @access private, so this is not a new stable public API surface.
• Remove the duplicate naive wp_split_selector_list() and call WP_Theme_JSON::split_selector_list() directly from the three states call sites. That function was new in 7.1, unshipped, and had no callers outside states.php.
• Add a regression test through wp_build_state_selector() for the attribute-string case (fails on the old splitter, passes now).

Trac ticket: https://core.trac.wordpress.org/ticket/65669

Use of AI Tools

N/A

---

This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.

[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

Core Committers: Use this line as a base for the props when committing in SVN:

Props khokansardar.

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.

[github-actions]

Test using WordPress Playground

The changes in this pull request can previewed and tested using a WordPress Playground instance.

WordPress Playground is an experimental project that creates a full WordPress instance entirely within the browser.

Some things to be aware of

• All changes will be lost when closing a tab with a Playground instance.
• All changes will be lost when refreshing the page.
• A fresh instance is created each time the link below is clicked.
• Every time this pull request is updated, a new ZIP file containing all changes is created. If changes are not reflected in the Playground instance,
  it's possible that the most recent build failed, or has not completed. Check the list of workflow runs to be sure.

For more details about these limitations and more, check out the Limitations page in the WordPress Playground documentation.

Test this pull request with WordPress Playground.