[iOS] Fix bug when entering split screen while fullscreen is active

The root cause of the bug was that, when split screen became active, the
primaryToolbarOffsetConstraint.constant was set to the new value first,
but then -addConstraintsToPrimaryToolbar created a new constraint,
resetting the constant value back to 0.

This CL fixes the bug by updating the tab strip and toolbar whenever
changing from compact to non-compact toolbar in either direction,
instead of only when going from compact to non-compact.

Fixed: 380111582
Change-Id: I7c92069bf70006efa8f420a0932a3a76824facde
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6039719
Commit-Queue: Robbie Gibson <rkgibson@google.com>
Reviewed-by: Federica Germinario <fedegermi@google.com>
Cr-Commit-Position: refs/heads/main@{#1386283}