Video editing in the media modal:

* Add a state: `Add Subititles`
* Add `text/vtt` to the list of allowed mime-types, files end in `.vtt`. `.srt` files are served as `text/plain`.
* The content body of a video shortcode should be used for adding `<track>` elements only. This happens dynamically in the modal. If added by hand, they can still be parsed and managed.

See #27016.


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git-svn-id: http://core.svn.wordpress.org/trunk@27325 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Admin Menu: Set default value of `$icon_url` in `add_menu_page()` to `dashicons-admin-generic`, fixes #26630.
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Editor: Show 'View Post' for any post the author can read.

This expands it to private posts and matches the logic in the toolbar.

props mordauk, SergeyBiryukov.
fixes #27059.

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git-svn-id: http://core.svn.wordpress.org/trunk@27327 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Allow for custom authentication handlers for all requests.

Turn the logic used by wp_get_current_user() into a determine_current_user filter.

props rmccue.
fixes #26706.

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git-svn-id: http://core.svn.wordpress.org/trunk@27328 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Adjust the height of the header and footer in the Find Posts modal on the Media Library screen, see #26952
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git-svn-id: http://core.svn.wordpress.org/trunk@27329 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Playlists:

* Add an action, `wp_playlist_scripts`, where a user can turn off all default script and style loading for playlists and roll their own.
* Move the script and style loading for playlists to a function, `wp_playlist_scripts( $type )`, that hooks into `wp_playlist_scripts`.
* Make the `<noscript>` playlist output an `<ol>`, instead of a list of links with no surrounding markup.

See #26631.


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git-svn-id: http://core.svn.wordpress.org/trunk@27330 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Update the UI styles for Playlist Settings.

Props melchoyce for the design.
See #26631.


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git-svn-id: http://core.svn.wordpress.org/trunk@27331 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Add a filter and document it: `playlist_styles`. Allows users to roll their own playlist themes.

Props DrewAPicture for the docs.
See #26631.


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git-svn-id: http://core.svn.wordpress.org/trunk@27332 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Add a class, `wp-playlist-playing`, to the currently loaded track when tracks are displayed. Add some subtle styles for light and dark playlist themes.

See #27321.


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git-svn-id: http://core.svn.wordpress.org/trunk@27333 1a063a9b-81f0-0310-95a4-ce76da25c4cd
A string was missing its translation wrapper in the Underscore template for video details.

Props Jayjdk.
See #27016.


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