[Browser UI] Introduce TabListBridge

Introduce a new class, TabListBridge, which implements the new
TabListInterface and is owned by BrowserWindowFeatures. This is a step
towards being able to use this class in shared code on the experimental
desktop android platform, such as in extension APIs.

This CL introduces the class and implements a single method, GetTab().
Following CLs will add more capabilities to the class.

Bug: 427503497
Change-Id: I13207fa3c86116ae8257fb2b7d5ea796ccfce2dd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6664924
Reviewed-by: Erik Chen <erikchen@chromium.org>
Reviewed-by: Calder Kitagawa <ckitagawa@chromium.org>
Auto-Submit: Devlin Cronin <rdevlin.cronin@chromium.org>
Commit-Queue: Devlin Cronin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1480760}