[iOS] Add nav bar to account switching menu view.

The account switching view controller has a nav bar.
The nav bar has a close button on iPhones only on the top right corner.

This CL adds these two properties to the view controller.

Bug: 336719423
Low-Coverage-Reason: TESTS_IN_SEPARATE_CL
Change-Id: I1418407f6e7b6df27035b6d7f8da4d3222e17271
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5593784


Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Reviewed-by: Arthur Milchior <arthurmilchior@chromium.org>
Commit-Queue: Jood Hajeer <jood@google.com>
Cr-Commit-Position: refs/heads/main@{#1311972}