[iOS] Add meaning to "Enter" passphrase button string

The "Enter" button on the passphrase infobar and passphrase settings is
not translated to the correct local language for these two specific
strings.
A string meaning is added to give context to the translators, and to
decouple it from the keyboard "Enter" string. (See attached bug for more
details).

Fixed: 371620885
Change-Id: Ie1ca5e082385bd621674c32c7d40965979e1f9af
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5928746
Reviewed-by: Marc Treib <treib@chromium.org>
Commit-Queue: Jood Hajeer <jood@google.com>
Cr-Commit-Position: refs/heads/main@{#1368731}