[flexiglass] Fixes long-press on emergency button.

Note: the long-press still doesn't do anything because the code in the
BouncerActionButtonInteractor code path for long-press checks
EmergencyAffordanceManager.needsEmergencyAffordance that returns false
but I made sure that the long-press action _is_ triggered.

As it turns out, adding a combinedClickable to a Material Button doesn't
work because the Material Button already sets clickable on its Surface
which prevents the touch from ever getting to the combinedClickable.

Unfortunately, rolling my own simplified button was the only path
forward.

Fix: 369767936
Test: manually verified that a single click still opens the emergency
call activity
Test: manually verified that long-press triggers the right code path;
even if it's not currently working (it also doesn't work in
pre-flexiglass/legacy)
Flag: com.android.systemui.scene_container

Change-Id: I1e684ba2df012c0416b0f50723a82fbd9cb3b8f9