[Tab Highlighting] Clear multi-selection when adding tabs and remove closed tab from multiselection.

Update tab model logic to ensure multi-selected tabs are deselected when
they are closed. Also, clear any existing multi-selection state when a
new tab is added to the model. This centralizes the multi-selection
clearing logic within the tab model operations.

Change-Id: Iff09ea49b81f63c7785321bc40d3d795511d15ad
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6870850
Auto-Submit: Hitarth Kothari <hitarthkothari@google.com>
Commit-Queue: Hitarth Kothari <hitarthkothari@google.com>
Reviewed-by: Calder Kitagawa <ckitagawa@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1504653}