Add `public` access modifier to methods/members of `WP_Widget` and `WP_Widget_Factory`.

See #27881, #22234.

Built from https://develop.svn.wordpress.org/trunk@28527


git-svn-id: http://core.svn.wordpress.org/trunk@28353 1a063a9b-81f0-0310-95a4-ce76da25c4cd