Update Rear Display Mode UX

Updates the Rear Display Mode UX such that after switching to the
Rear Display Mode, the inner display shows a dialog letting the user
know that the content has moved to the other display.

Bug: 371095273

Flag: android.hardware.devicestate.feature.flags.device_state_rdm_v2

Test: demo app
Test: atest com.android.systemui.reardisplay
Test: atest com.android.systemui.display.domain.interactor

Change-Id: I499f268f8a4cf1c290501951bdc387c133a63f22