Expose the MediaFrame.MediaFrame frame via a ready trigger

[soulseekah]

It is currently impossible to grab the initial "manage" View (Frame) (which contains all the other Subviews).

Use case: I'd like to make modifications to the modal, add some event handlers, which I'm unable to do reliably I have nothing to do .on() with.

I have to wait for some of the components to appear. That means looping or other dirty hacks. I propose to trigger a DOM even on the initial container.

With the attached patch I can do something like:

jQuery( document ).on( 'wp-media-grid-ready', '##wp-media-grid', function( e, frame ) {
    frame.on( 'edit:attachment', function() {
        // Code that runs when the modal is being opened.
    }
} );

Related #35205

[SergeyBiryukov]

In 47807:

Media: Expose media grid frame via wp-media-grid-ready trigger for easier customization.

Props soulseekah.
Fixes #50185.

[desrosj]

This received a call out in the Miscellaneous Developer Changes in 5.5 dev note: ​https://make.wordpress.org/core/2020/07/29/miscellaneous-developer-focused-changes-in-wordpress-5-5/.