Using onLongPress from detectTapGestures in LockscreenTouchHandling.

When using the custom detectLongPressGesture detector, the long-press
gesture is directed to both
KeyguardQuickAffordanceViewBinder#OnLongClickListener and
KeyguardTouchHandlingViewModel#onLongPress. The modifier depends on a
timer, rather than the consumption of down events by lower surfaces in
the UI hierarchy, making it difficult to separate responsibilities of
gesture handling.

Using the onLongPress callback of detectTapGestures, long-press events
are directed to single UIs and resolves the conflict.

Test: manual. Verified long-press is handled by shortcuts when
  long-pressing their icons and that the lockscreen does not react to
  the event.
Test: manual. Verified long-press continues to behave as expected on any
  other surface of the lockscreen
Test: manual. Disabled long-press in
  vendor/unbundled_google/packages/SystemUIGoogle/res/values/config.xml
  and verified that taps and double taps are still processed by the
  lockscreen
Bug: 436334214
Flag: com.android.systemui.scene_container

Change-Id: Idcfcc5bc0df1990bcbaf7c55c6304ca4b23408ef