Widget Customizer: Improve widget search.

* Removes jQuery.liveFilter dependency
* Filters widget collection directly
* Widget's name, ID and description will be searched

fixes #27451.
Built from https://develop.svn.wordpress.org/trunk@27650


git-svn-id: http://core.svn.wordpress.org/trunk@27493 1a063a9b-81f0-0310-95a4-ce76da25c4cd