Add support for `WP_Error` objects passed to `wp_send_json_error()`. The error object gets output as an array of error codes and messages, rather than as an empty object.

Fixes #28978
Props paulschreiber


git-svn-id: https://develop.svn.wordpress.org/trunk@30506 602fd350-edb4-49c9-b593-d223f7449a82
Update the inline docs for `wp_die()` to reflect parameter changes made in r30355

See #10551


git-svn-id: https://develop.svn.wordpress.org/trunk@30507 602fd350-edb4-49c9-b593-d223f7449a82
Abstract the theme browser route paths into attributes so they can be easily overridden.

Fixes #30116
Props matveb


git-svn-id: https://develop.svn.wordpress.org/trunk@30508 602fd350-edb4-49c9-b593-d223f7449a82