Customizer: Prevent double-encoding in `WP_Customize_Control`.

Control's label and description may include HTML.

fixes #29572.
Built from https://develop.svn.wordpress.org/trunk@30326


git-svn-id: http://core.svn.wordpress.org/trunk@30325 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Improve keyboard accessibility on Custom Header and Custom Background screen.

props florianziegler.
fixes #29289.
Built from https://develop.svn.wordpress.org/trunk@30327


git-svn-id: http://core.svn.wordpress.org/trunk@30326 1a063a9b-81f0-0310-95a4-ce76da25c4cd