Docs: Synchronize and correct documentation for various metadata functions and filters.

Follow-up to [47390], [47611], [48192], [48402].

See #49572, #43941, #45464.
Built from https://develop.svn.wordpress.org/trunk@48411


git-svn-id: https://core.svn.wordpress.org/trunk@48180 1a063a9b-81f0-0310-95a4-ce76da25c4cd