Similarly to `doc_paintTile` in init.cxx, we can't use the regular initialization for our graphics backend on iOS. If we do so, we render a completely white area. Instead, we need to use CoreGraphics, which is the iOS library for rendering graphics Change-Id: I94cb620d422c02f8343db30eea24cecc53d928c6 Reviewed-on: https://gerrit.libreoffice.org/c/core/+/185095 Tested-by: Jenkins Reviewed-by: Miklos Vajna <vmiklos@collabora.com>