Customize: Ensure that widgets and nav-menus can be closed after entering content.

Previously, the ⌧ button would close the search panel, or remove the results. This restores that, in addition pressing escape will do the same.

Fixes #48198.

Props garrett-eclipse, tobifjellner, afercia, JavierCasares.


Built from https://develop.svn.wordpress.org/trunk@48461


git-svn-id: https://core.svn.wordpress.org/trunk@48230 1a063a9b-81f0-0310-95a4-ce76da25c4cd