[Focus] Ensuring that Temporary Groups Dissolve on Unfocus

There are numerous ways that temporary tab groups can become unfocused,
so it would be infeasible to update all of these exit points to dissolve
the tab groups. Instead, this CL enforces that (almost) all of the exit
points call ExitFocusMode with a specific exit reason. This consolidates
metrics collection and allows the logic to dissolve temporary groups to
apply everywhere.

One intricacy is that in tab group focus mode, a user can move all the
tabs in the group to a new window, which preserves the focus state.
However, that doesn't really make sense for non group focus mode since
the new state would have no tabs besides the ones in focus selection
mode. So, the new tabs are kept as normal tabs when they are moved.

Bug: 563374521
Change-Id: Ib451c8e753201f5e5592e464cea9872dd6528f5d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/8427727
Reviewed-by: Eshwar Stalin <estalin@chromium.org>
Commit-Queue: Kunal Daftari <kunaldaftari@google.com>
Cr-Commit-Position: refs/heads/main@{#1703163}