Themes whose `wp-content/themes/<dirname>` include valid non-alphanumeric (cross-platform) characters work for non-block themes, but did not previously resolve for block themes. For example, a block theme in `wp-content/themes/twentytwentytwo-0.4.0/` directory resulted a 404 "No route was found matching the URL and request method" response when attempting to customize it in the Site Editor.
This commit adds support for the following characters in a theme's root directory: `_`, `.`, `@`, `[`, `]`, `(`, and `)`. Subdirectory themes and `-` are already supported.
Follow-up to [51003], [52051], [52275].
Props mkaz, costdev, hellofromTonya, jffng, justinahinon, peterwilsoncc, spacedmonkey, TimothyBlynJacobs.
Fixes#54596.
Built from https://develop.svn.wordpress.org/trunk@52376
git-svn-id: http://core.svn.wordpress.org/trunk@51968 1a063a9b-81f0-0310-95a4-ce76da25c4cd