Fixes the rendering of spreadsheets in the iOS app. (The cell area was
rendered at half the scale of the row and column headers.)

Actual code change only in desktop/source/lib/init.cxx, but update
related comments elsewhere to mention CoreGraphics, too, and not just
cairo.

Change-Id: Ife99c6a2d58e592cfea3b4ed1ab09c19fba77e72
(cherry picked from commit 3ace447b)
Reviewed-on: https://gerrit.libreoffice.org/63919
Tested-by: Jenkins
Reviewed-by: Tor Lillqvist <tml@collabora.com>