[iOS] Handle Tab selection from the TabGroup

Pass a delegate to the BaseGrid in the TabGroup.
Also, removes two methods from the BaseGrid delegate that are unused.

https://screencast.googleplex.com/cast/NDc5MTEwNzI3NDY3MDA4MHxjYjIwYTRhYi1jMQ

Fixed: 331747131
Change-Id: I01099a1d38c57e422a04735f008b8775fbf9dcd0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5435237


Auto-Submit: Gauthier Ambard <gambard@chromium.org>
Reviewed-by: Jesse Doherty <jwd@chromium.org>
Commit-Queue: Jesse Doherty <jwd@chromium.org>
Reviewed-by: Aliona Dangla <alionadangla@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1283980}