[iOS] Add web view resizing enum

Add the enum in a separate CL in order to use it in internal.

This is part of multiple changes:
1) https://crrev.com/c/6973698 (Current)
2) https://crrev.com/i/8609417
3) https://crrev.com/c/6853827
4) https://crrev.com/c/6839620

Bug: 438144976
Change-Id: Id83c656ab8431c408c9d77553660dc07995fa892
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6973698
Commit-Queue: Aliona Dangla <alionadangla@chromium.org>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1519415}