Don't overwrite the `length` property unnecessarily when generating metadata for audio and video files.

Props jrf, wonderboymusic.
Fixes #29176.

Built from https://develop.svn.wordpress.org/trunk@29728


git-svn-id: http://core.svn.wordpress.org/trunk@29502 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Media: revert enabling of multi-file uploading for mobile devices. Currently only iOS Safari supports it but has a bug that prevents uploading of videos. Fixes #29602
Built from https://develop.svn.wordpress.org/trunk@29729


git-svn-id: http://core.svn.wordpress.org/trunk@29503 1a063a9b-81f0-0310-95a4-ce76da25c4cd
TinyMCE: fix image captions regexp when wpautop is disabled in wp_editor(). Fixes #29592 for trunk.
Built from https://develop.svn.wordpress.org/trunk@29730


git-svn-id: http://core.svn.wordpress.org/trunk@29504 1a063a9b-81f0-0310-95a4-ce76da25c4cd