Closes#43171
Previously the tab switcher only subscribed to events from a single pane
so closing tabs in other panes wouldn't cause the tab switcher to
update. This PR changes that so the tab switcher subscribes to the whole
workspace and thus updates when tabs in other panes are closed.
It also modifies the work in #44006 to sync selected index across the
whole workspace instead of just the original pane in the case of the
all-panes tab switcher.
Release Notes:
- Fixed all-panes tab switcher not updating in response to changes in
other panes
40a611bf34