Add missing DocBlocks for several functions in wp-admin/includes/ms.php.

Props dustyf.
See #30483.

Built from https://develop.svn.wordpress.org/trunk@30630


git-svn-id: http://core.svn.wordpress.org/trunk@30620 1a063a9b-81f0-0310-95a4-ce76da25c4cd
WPDB Unit Tests: Fix a fatal error that occurs in the `test_strip_invalid_text()` test if the `mbstring` extension isn't activated in PHP.

Built from https://develop.svn.wordpress.org/trunk@30631


git-svn-id: http://core.svn.wordpress.org/trunk@30621 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Document the `$user_id` parameter added to the 'admin_color_scheme_picker' hook in 3.8.1.

Props Ipstenu.
Fixes #30551.

Built from https://develop.svn.wordpress.org/trunk@30632


git-svn-id: http://core.svn.wordpress.org/trunk@30622 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Remove return descriptions from the DocBlocks for `add_image_size()` and `set_post_thumbnail_size()` as they don't return anything.

Also document the `$_wp_additional_image_sizes` global, leveraged in `add_image_size()`.

Props stevegrunwell.
Fixes #30511.

Built from https://develop.svn.wordpress.org/trunk@30633


git-svn-id: http://core.svn.wordpress.org/trunk@30623 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Upgrade to MediaElement 2.16.2
https://github.com/johndyer/mediaelement/compare/2.15.1...2.16.2

Fixes #30281.

Built from https://develop.svn.wordpress.org/trunk@30634


git-svn-id: http://core.svn.wordpress.org/trunk@30624 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Remove an invalid parameter from the DocBlock for the `gallery_style` hook.

Props keesiemeijer.
Fixes #30507.

Built from https://develop.svn.wordpress.org/trunk@30635


git-svn-id: http://core.svn.wordpress.org/trunk@30625 1a063a9b-81f0-0310-95a4-ce76da25c4cd