Call KeyguardViewMediator#hideWithAnimation on the main thread

This CL ensures that we call KeyguardViewMediator#hideWithAnimation on
the main thread when animating an app launch.

This CL also changes how this method operates: it now relies on
 #keyguardDonePending being called beforehand. This ensures that
keyguardDone() is actually called before hiding the keyguard, which was
not the case with the previous implementation.

Bug: 184726377
Test: Click a notification on lockscreen (without security)
Change-Id: Ic391e28066282e059e57cc50c5191e50ca7df06e