Ensure RDM dialog is shown after screen off/on

Turning off the display dismisses the RDM dialog. However, when the
device turns on again, the device is still in the RDM state. In this
case, we should re-show the RDM dialog once Keyguard is dismissed.

Fixes: 394228925
Flag: EXEMPT bugfix
Test: manual
Test: atest RearDisplayCoreStartableTest
Change-Id: Id9c80a870ed27099f2ce809c4b7ce452f108bfa7