Fix bug with over-expanding split task tile

This CL changes GroupedTaskView#onMeasure() to return more robustly in the case where a single task from a GroupedTaskView is staged.

See bug for fine details, but basically we no longer allow onMeasure() to re-bound the split task to fullsize in split selection state -- we leave it in half size all the time (with scale and translation applied). To allow it to stay scaled-up and translated properly across rotations and stuff, we now avoid resetting translation and scale until split select is exited.

Fixes: 365476600
Test: Manual test with offscreen tiles, rotations, fake landscape and seascape
Flag: NONE bugfix
Change-Id: I0ee8d13d310ed1f134f3f396bb87541a5ea685ef