ConfirmationDialog: Fail if accessibility services are running.

As the confirmation dialog only has limited accessibility support it
may not be usable by users requiring accessibility services.

Therefore, if the user has enabled accessibility services, fail with
ConfirmationNotAvailableException so the application can handle this
case. Also document this behavior.

Bug: 74545109
Test: Manually tested.
Change-Id: Ibfb80d217f5cbdc9ec2f4e0432dfdd88add69703