Improve keyboard control of Edit Selection mode in the media manager.

See #29326
Props adamsilverstein

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git-svn-id: http://core.svn.wordpress.org/trunk@30371 1a063a9b-81f0-0310-95a4-ce76da25c4cd
WPDB: When a `db.php` drop-in is being used, and it doesn't explicitly define itself as connecting to MySQL, skip the character set checks. This ensures that existing drop-ins won't accidentally run checks that they don't support.

See #21212.

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git-svn-id: http://core.svn.wordpress.org/trunk@30372 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Improve Thickbox's close button so it can be announced by screen readers.

Fixes #29455
Props SergeyBiryukov

Built from https://develop.svn.wordpress.org/trunk@30376


git-svn-id: http://core.svn.wordpress.org/trunk@30373 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Avoid re-registering the `keydown` event controller in the media grid so arrow controls don't skip media items.

Fixes #30348
Props UmeshSingla

Built from https://develop.svn.wordpress.org/trunk@30377


git-svn-id: http://core.svn.wordpress.org/trunk@30374 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Update the inline docs for the `keyEvent` callback in the media grid.

Props adamsilverstein
See #29725

Built from https://develop.svn.wordpress.org/trunk@30378


git-svn-id: http://core.svn.wordpress.org/trunk@30375 1a063a9b-81f0-0310-95a4-ce76da25c4cd