General code cleanup and improving video sizing in the admin:

* Abstract the setting of a primary button and its callback in `wp.media.view.MediaFrame.MediaDetails`
* Account for the existence or non-existence of `$content_width` in the TinyMCE views for video
* Make sure video models always have dimensions, even if they are the defaults
* For browsers that are not Firefox, don't use a timeout when setting the `MediaElementPlayer` instance in TinyMCE views

See #27320.


Built from https://develop.svn.wordpress.org/trunk@27655


git-svn-id: http://core.svn.wordpress.org/trunk@27498 1a063a9b-81f0-0310-95a4-ce76da25c4cd