[iOS] Support dynamic type in Omnibox Shortcuts.

Adds support for dynamic type (changing font size for a11y):
- Update the popup and the shortcuts view controllers to react to font
size changes
- Shortcuts collection view now doesn't use two sections, instead all
items are in the same section and the indices are used.

Bug: 937782
Change-Id: Ie3432d13aa44e66d1f1d509441e1ad5fc1a2500c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1535890
Reviewed-by: Yi Su <mrsuyi@chromium.org>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Stepan Khapugin <stkhapugin@chromium.org>
Auto-Submit: Stepan Khapugin <stkhapugin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#645415}
5 files changed