Help/About: Update videos and their descriptions on the About page.

Follow-up to [48675], [48686], [48721], [48729], [48730], [48736].

Props ryelle, marybaum, estelaris, desrosj, joen, afercia.
Reviewed by jorbin, SergeyBiryukov.
Merges [48761] to the 5.5 branch.
See #50416.
Built from https://develop.svn.wordpress.org/branches/5.5@48763


git-svn-id: https://core.svn.wordpress.org/branches/5.5@48525 1a063a9b-81f0-0310-95a4-ce76da25c4cd