If the font face doesn't include a Bold or Italic version, we still want
to display the font as bold/italic, so we fake it with freetype.
This also prevents recurring error messages where the outline font warns
about "substitutes" within the same font family.
Also allows variants on the weight descriptor to be used without
throwing a substitution warning
Fixes https://gitlab.com/kicad/code/kicad/issues/13654
Seth Hillbrand
Ola Rinta-Koski
jean-pierre charras
Jeff Young