Adds call to rear display overlay intent

When a request is made to enable rear display
mode, and it's from a process that doesn't
hold the CONTROL_DEVICE_STATE permission, we
should launch the educational overlay to alert
the user of what's about to happen.

This change also introduces a method on
DeviceStateManagerGlobal and Service to allow
the overlay activity to communicate back to the
system service if the overlay has been dismissed
or acted on

Bug: 207686851
Test: DeviceStateManagerServiceTest
 && DeviceStateManagerGlobalTest
Change-Id: Ife7d642563005a2571bdeacbd7a3baaa9aad5e25