NanoSVG does handle opacity (thanks Mark) but the check needs to be
unsigned if we are comparing the resulting down-shifted value against
zero
Fixes https://gitlab.com/kicad/code/kicad/issues/13033
It might make sense to do that with board and/or schematic items for
hit-testing or something, but it definitely doesn't make any sense for
the drawing sheet border.
Also, when reading in items with a transparent fill, treat them as
unfilled (otherwise we get filled with layer colour in at least PCBNew).
* Do not compile dxf old files.
* import gfx, gal mode: make absolute placement working.
* Import gfx in legacy canvas: use it and make interactive placement working
* Take imported line width in account. Ensure DXF line thickness is OK.
* handling empty files in legacy mode.