[TabAlert] Subscribe to GlicTabIndicatorHelper for glic tab alerts

The TabAlertController was originally subscribed to the GlicKeyedService
for tab pinning and focus changes in order to determine when a glic tab
alert is active. This logic already exists in the GlicTabIndicatorHelper
and shouldn't be duplicated in the TabAlertController in case the
conditions in which an alert is active changes.

This CL allows the TabAlertController to subscribe to the
GlicTabIndicatorHelper to be notified when a glic alert changes so that
the controller can forward tab alert changes to UI if necessary.

Bug: 422748580
Change-Id: Ibc1c2b8362babd04378b19a110cf0af38dff80db
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6842648
Reviewed-by: David Pennington <dpenning@chromium.org>
Commit-Queue: Steven Luong <stluong@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1501424}