Media Grid: Manage focus when toggling between the grid and an edit attachment modal

Props adamsilverstein for the initial patch.
Fixes #28857.

Built from https://develop.svn.wordpress.org/trunk@29282


git-svn-id: http://core.svn.wordpress.org/trunk@29064 1a063a9b-81f0-0310-95a4-ce76da25c4cd
The Underscore templates for Gallery settings should respect defaults when marking an `<option>` as `selected`.

See #28693.

Built from https://develop.svn.wordpress.org/trunk@29283


git-svn-id: http://core.svn.wordpress.org/trunk@29065 1a063a9b-81f0-0310-95a4-ce76da25c4cd
When gallery settings are overridden, the JS-generated shortcodes need to check the new defaults before deleting attributes that it suspects are the same as the original default values.

`wp.media.collection` has a new method to do this: `setDefaults()`.	Also flips the use of `_.extend` to allow this method to be overriden on instance creation.

See #28693.

Built from https://develop.svn.wordpress.org/trunk@29284


git-svn-id: http://core.svn.wordpress.org/trunk@29066 1a063a9b-81f0-0310-95a4-ce76da25c4cd