Reset keyguard drawn tasks in onScreenTurnedOff

Resets keyguard drawn tasks in onScreenTurnedOff
callback instead of onScreenTurnedOn callback.

This is necessary to avoid clearing of the tasks
on the first boot when onScreenTurnedOn is called
immediately after onScreenTurningOn from the WM
side (without waiting for the SystemUI drawn
callback).

Bug: 268144550
Test: manual fold/unfold
Test: check boot time with/without fix
Test: atest com.android.keyguard.mediator.ScreenOnCoordinatorTest
Change-Id: I780e2738ed2fcf8ec013058a2212612fb6874288