Extract some dummy implementations for XCanvasFont methods from cairocanvas::CanvasFont to a new CanvasFontBase base class. That will allow reusing them in other XCanvasFont implementations that currently have equivalent implementations for those methods by themselves. That allows to deduplicate code a bit. Change-Id: I964330de605368eaa665c1ddc60db7b6e45d9fcb Reviewed-on: https://gerrit.libreoffice.org/c/core/+/208848 Tested-by: Jenkins Reviewed-by: Michael Weghorn <m.weghorn@posteo.de>