Some class names with HTML character references could be mishandled, for example: - Failure to remove an existing class like `&` with `::remove_class( '&' )` - Double-encoding of an existing class like `&` after a modification, becoming `&` The second case manifested after double-encoding prevention was removed from `::set_attribute()` in [60919]. Developed in https://github.com/WordPress/wordpress-develop/pull/10591. Props jonsurrell, dmsnell. Fixes #64340. Built from https://develop.svn.wordpress.org/trunk@61346 git-svn-id: http://core.svn.wordpress.org/trunk@60658 1a063a9b-81f0-0310-95a4-ce76da25c4cd