focus-mode: Hide QS tile for ephemeral accounts

This CL fixes a crash when trying to access focus mode on a guest
account by removing access to the focus mode feature.

The Focus Mode feature should only be available to regular and child
accounts. Ephemeral accounts (guest, public, kiosk, etc.) should be
excluded.

Bug: b/344040908
Test: added a new test
Change-Id: I7d8ee8b1d0aa7abe07734a2a28b7ca88aaa59358
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5601705


Reviewed-by: Sean Kau <skau@chromium.org>
Commit-Queue: Richard Chui <richui@chromium.org>
Reviewed-by: Yongshun Liu <yongshun@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1311723}