When an HTML5 fallback button is pressed in the Audio or Video Details state, filter the library by that specific mime-type when the Add Audio|Video Source is activated.

See #27389.


Built from https://develop.svn.wordpress.org/trunk@27658


git-svn-id: http://core.svn.wordpress.org/trunk@27501 1a063a9b-81f0-0310-95a4-ce76da25c4cd
When inserting a video shortcode into the editor, set the `poster` attribute automatically if the video has a featured image attached to it.

See #27460.


Built from https://develop.svn.wordpress.org/trunk@27659


git-svn-id: http://core.svn.wordpress.org/trunk@27502 1a063a9b-81f0-0310-95a4-ce76da25c4cd