I18N: Mark the strings with plugin and theme names in email notifications for translation.

Follow-up to [48517].

See #50350.
Built from https://develop.svn.wordpress.org/trunk@48519


git-svn-id: https://core.svn.wordpress.org/trunk@48281 1a063a9b-81f0-0310-95a4-ce76da25c4cd