Update rear display tests to work for any device state

We currently check for a configuration change to
occur to verify that the device has actually
moved the system to the rear display when display
mode is enabled. This adds better checks and logic
to be able to test the rear display feature on
any type of device and on any device state.

Bug: 281952366
Test: ExtensionRearDisplayTest
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:ab34d4c496a5e673a7d4fb5d939e2ad9b46da683)
Merged-In: Idfdad7aaa42f3ea33ab3c9917796614be2292599
Change-Id: Idfdad7aaa42f3ea33ab3c9917796614be2292599