Use proper non-capturing regex syntax for YouTube in `wp_video_shortcode()`.

Props Fab1en.
See [27063].
Fixes #29119.

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Don't show the Featured Image metabox for users with the `contributor` role. Do enqueue media so that TinyMCE previews work for YouTube embeds, etc.

Props SergeyBiryukov.
Fixes #28327.

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In `media.view.BulkSelectionActionButton.click()`, do not assume that `delete` is the only possible bulk action.

Fixes #29101.

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Ignore entities in XML-RPC requests.

props mdawaffe, nacin.

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4.0-beta3

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Media Grid: display upload errors in a dismissable sidebar.

See #29037.

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Media Grid: after [28996], use the same cover size for audio/video files that images use for thumbnails.

See #24716.

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