Flesh out and fix formatting in the DocBlock for `wp_register_widget_control()`.

Includes:
* Added todos for documenting `$options` in the hash notation style
* Backtick-escaping and general formatting

See #30315.

Built from https://develop.svn.wordpress.org/trunk@30778


git-svn-id: http://core.svn.wordpress.org/trunk@30768 1a063a9b-81f0-0310-95a4-ce76da25c4cd