[iOS] When opening the TabGrid move the active tab to the middle

When the tab grid is opened, the active tab or tab group is currently
moved to the top of the screen.
However, it is more natural to have it in the middle.

Fixed: 428756505
Change-Id: Iee58df3f0ab39c97d948d8ff290766a69f1e8eb3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6769580
Reviewed-by: Louis Romero <lpromero@google.com>
Auto-Submit: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Louis Romero <lpromero@google.com>
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1488708}