Fix overscroll doesn't affect scrolling when released

Bug: 188531406

When an EdgeEffect is flung past 0 into negative values, it
shows a stretch from the other side. To prevent this, the EdgeEffect
animation is now terminated when it reaches 0. I also made it so
that dragging to a value of 0 releases the EdgeEffect.

I also fixed the nested scrolling so that the stretch release
of ListView occurs before the onNestedPreScroll().

Test: new tests and manual testing
Change-Id: Ia20a6b96d25cf31ef143511828ddce5c33cee804