sc tiled rendering: Simplify the zoom computation.
sc tiled rendering: Simplify the zoom computation.

In principle, we should avoid messing up with zoom, and instead just work with
the MapMode, but we are not there yet - lots of places are hardcoded to work
in pixels.

Change-Id: I572b0d54fbfc72494c44ef95e7fda5e655f83fde

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core