Avoid re-registering the `keydown` event controller in the media grid so arrow controls don't skip media items.

Fixes #30348
Props UmeshSingla

Built from https://develop.svn.wordpress.org/trunk@30377


git-svn-id: http://core.svn.wordpress.org/trunk@30374 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Update the inline docs for the `keyEvent` callback in the media grid.

Props adamsilverstein
See #29725

Built from https://develop.svn.wordpress.org/trunk@30378


git-svn-id: http://core.svn.wordpress.org/trunk@30375 1a063a9b-81f0-0310-95a4-ce76da25c4cd