Refactor AbsListView position scrollers for better abstraction

The AbsListView sub-scroller knows nothing about layout. That's now
handled by ListView and GridView, with subclasses of AbsListView using
the default PositionScroller. Removes unnecessary (unreleased) APIs.

Also fixes a bounds check that was using the item position rather than
the child view position.

BUG: 13006641
Change-Id: I2adb0f15623e32295facf81f5ada974083ba03ce