[iOS][WidgetKit] Add meaning and char limit to strings

Also fixes string with "\n" as part of it.

Bug: 1138717
Change-Id: Id87562a1d2896d8cacceac5a3c95af8d7713e91a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2521295


Reviewed-by: Olivier Robin <olivierrobin@chromium.org>
Commit-Queue: Javier Flores <javierrobles@chromium.org>
Cr-Commit-Position: refs/heads/master@{#824931}