Pinned tab addition to new tab group in another window

A pinned tab added to a tab group in another window
was being linked to last the tab.

Solution was to keep track of tab indices to make sure
we do not lose them and with pin tabs unpin them before
adding to a tab group from another window.
Added unit tests as well.

Bug: 40872481
Change-Id: I43c5ebec7362f77852fa5f99dab4dde76d9bc676
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6165744
Commit-Queue: Muhammad Salmaan <musalmaan@chromium.org>
Reviewed-by: Dana Fried <dfried@chromium.org>
Reviewed-by: Taylor Bergquist <tbergquist@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1413059}