Move ScrollView scroll capture to the center

Avoid most floating content by centering the requested content within
the view instead of just scrolling so that it's visible.

See ag/14213766 for the corresponding RecyclerView change.

Bug: 189487659
Test: atest ScrollViewCaptureHelperTest, plus manual testing.
Change-Id: I194288cf9e568614ffd7c45b7d046a5b982829d6