[Flexiglass] Handle remoteInput scrolling for nested notifications

The previous code was not accounting for children inside notification
groups, so the calculated scroll offset was not enough for these
notifications, because it was only the y translation of the row related
to its parent.

Bug: 431275624
Test: click the remoteInput of a nested notification -> stack scrolls to
bring the IME to a visible position
Flag: com.android.systemui.scene_container

Change-Id: I2ac6a5006e727874cac483c269e42fed3d94fa58