Placeholder implementation of stretch overscroll using offset

Temporarily use an offset RenderEffect for the stretch overscroll.
This makes it possible to visually validate the effect and start
writing CTS tests to ensure it is functioning.

Bug: 178807038
Test: Iab32812bfa626ae6932f52c1a9af78069b5dc6ac
Change-Id: I5b0da0e669d36f4149cd58b4b3aff149a1fa7e14