Fixing QS expanding in split shade when swipe happens on notifications

Now QuickSettings expand only when swipe begins on them, measured by
initial touch X position.
NSSL is receiving touches correctly from NotificationPanelViewController
(shouldn't be intercepted) but then if nothing wants to handle that
internally, it's passing it back to OnOverscrollTopChangedListener where
we are aware of split shade mode and can cancel expansion of quick settings.

Bug: 181235927
Test: manual
Change-Id: Ic288c468770bf199435fed9a0896f757e41fa721