Previously, a 600 DPI was used to set device scale (can create minor visible rounding issues).
Using now 4800 DPI to reduce these rounding artifacts.
Fixes: lp:1845229
https://bugs.launchpad.net/kicad/+bug/1845229
CAIRO_PRINT_CTX provides a Cairo context created from wxPrintDC.
It allows one to prepare printouts using the Cairo library and
let wxWidgets handle the rest.