Editor: Make some hardcoded strings in block patterns translatable.

Follow-up to [48726].

Props justinahinon, audrasjb, nabilmoqbel, tobifjellner, yoavf, ramiy.
Merges [48859] to the 5.5 branch.
Fixes #50845.
Built from https://develop.svn.wordpress.org/branches/5.5@48860


git-svn-id: https://core.svn.wordpress.org/branches/5.5@48622 1a063a9b-81f0-0310-95a4-ce76da25c4cd