DO NOT MERGE Cherry-Pick: Add ViewConfiguration.getScaledScrollFactor()

This value is used to convert ACTION_SCROLL axis values into raw
pixel distances.

CP of ag/1333603 from master to feldspar-dev. New method is @hide and
@SystemApi in this version. In master, it's part of the new public
API, but feldspar will launch before O.

Change-Id: I5ee73ebcd183c43939ae8aa157e88489e05d4760