[iOS] Change color of highlighted cell in file destination picker

This CL updates the background color of the file destination picker cell
when its highlighting state changes, to match the behaviour of the
identity button.

Video:
https://drive.google.com/file/d/1lpU8L7o0Sa66aROOTxHpwEy4cGLg9CYO/view

Bug: 325435476
Change-Id: Ifc9df6158606282edb1b2b9d7a12d35e9a77fda2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6149454
Auto-Submit: Quentin Pubert <qpubert@google.com>
Reviewed-by: Olivier Robin <olivierrobin@chromium.org>
Commit-Queue: Quentin Pubert <qpubert@google.com>
Cr-Commit-Position: refs/heads/main@{#1402969}