Set isSelected on StripLayoutTab as part of starting state

This ensures that keyboard focus states remain consistent when the selected tab is scrolled off screen.

Screencast after: https://screencast.googleplex.com/cast/NDkxNDYxODA3MjgyNTg1NnwxMzBlNWIxZS0xNQ

Screencast before: https://screencast.googleplex.com/cast/NjM2MDI5Njk1MTExOTg3Mnw0ODQyNWZkNi1hNA

Fixed: 419072631
Test: 
Change-Id: I70c01cda2dc88dacfce7cb045d31d26c2f96bc9d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6570950
Reviewed-by: Neil Coronado <nemco@google.com>
Commit-Queue: Jenna Himawan <jhimawan@google.com>
Cr-Commit-Position: refs/heads/main@{#1463509}