Add a debounce wrapper to the media grid search handler. The search callback is now fired after a 300 ms typing pause.
Remove redundant handlers for 'search' and 'change', preventing multiple/duplicate search callbacks.
Props certainstrings, joemcgill, Kelderic, batmoo.
Fixes#38911.
Built from https://develop.svn.wordpress.org/trunk@40060
git-svn-id: http://core.svn.wordpress.org/trunk@39997 1a063a9b-81f0-0310-95a4-ce76da25c4cd