Hardens the logic in Escalator scrolling (#13334)

Filtering a Grid broke Escalator's scrolling. This probably has to do
with several row-modifications combined with scrolling and adjustments.
The previous method had the possibility for ridiculous adjustments,
going out of bounds. This makes the changes absolute rather than
relative.

Change-Id: Id52f2d481bcaacf80af1c0e7ae28ac2ee3dbcae0