[flexiglass] Fix NSSL-Flexiglass touch in default case

Fixing onScrollTouch incorrectly setting mIsBeingDragged state (only applies to notifs with no defined onClick)
Also added missing call to reset current gesture overscroll state at the end of each gesture.

Bug: 339521136
Test: manually verified with logging that mIsBeingDragged state is now correct throughout swipe gestures
Flag: com.android.systemui.scene_container
Change-Id: I8a8384c3a74f837748ed92a77a036ec9798bb8d6