Add edge effect color APIs to ScrollViews

This CL adds APIs to ScrollView and HorizontalScrollView to
set edge effect colors.

Previously, edge effect fields were accessed via reflection
by many apps to obtain this functionality.
For apps targeting Q, those fields will not be accessible
anymore and instead we'll ask them to use the new APIs.

Bug: 123769386
Bug: 123768600
Bug: 124052619
Bug: 124053130
Test: HorizontalScrollViewTest, ScrollViewTest
Change-Id: I32cbf0b01658955d34662c9a9aaca87b54ab7706