Fix missing Notification collapse animation on LS

When we start to expand a Notification on the LS but we abort it
halfway, the Notification should animate back to the collapsed
state. This animation was missing, because we tried to access the
"ExpandableView#actualHeight" property via reflection.

Test: create a makepush build and observe the animation on the LS
Test: atest DragDownHelperTest
Test: atest PulseExpansionHandlerTest

Fixes: 237084760
Change-Id: I3798dec1ab016d89b61e87a3192199ea16181472