kiosk: enable toggle overview shortcut (F5)

Enable toggle overview shortcut when kiosk troubleshooting tools are
enabled.
Do not explicitly disallowed toggling overview for kiosk apps, but
catch the troubleshooting shortcuts (including toggling overview)
in kiosk even when the policy is disabled, but do nothing.

BUG=b/284118018
TEST=unit_tests
TEST=web/chrome app ash/lacros kiosk with/without troubleshooting tools

Change-Id: Iff230e036f1523435fcbe64236aa9d0a3db88179
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4562013


Commit-Queue: Polina Bondarenko <pbond@chromium.org>
Reviewed-by: Sammie Quon <sammiequon@chromium.org>
Reviewed-by: Sergii Bykov <sbykov@google.com>
Auto-Submit: Polina Bondarenko <pbond@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1148679}