More global event hooks using the media.events, like "modal:open", "modal:close", etc

[jtsternberg]

There seem to be plentiful hooks in the media backbone system, but most require listening to the frame/controller/etc vs having global hooks/events to listen to. This, obviously, would be much like WP's do_action. Each event should pass contextual info including the frame/controller/etc object.

Select2 (as well as most JS modal libs) provides an example of prior art: ​https://select2.github.io/examples.html#events

Using that implementation as an example, we could do something like:

wp:media:open is fired whenever the modal is opened. wp:media:opening is fired before this and can be prevented.

wp:media:close is fired whenever the modal is closed. wp:media:closing is fired before this and can be prevented.

wp:media:highlight is fired whenever a result is highlighted (clicked).

wp:media:unhighlight is fired whenever a result is unhighlighted.

wp:media:select is fired when a result is chosen and modal is closed. wp:media:selecting is fired before this and can be prevented.

wp:media:change is fired whenever the modal changes state. wp:media:changing is fired before this and can be prevented.

[jtsternberg]

https://core.trac.wordpress.org/ticket/27698 Is similar, and introduced wp.media.events which, I assume, is what we would use to create this API.