QFontDialog doesn't have the capability that KFontDialog had, where with
the latter when using adjustAllFonts() you could change only one of
the font family, the font style, the font size, e.g. you could change
the size and keep each respective font families for "General" and "Toolbar" as is.
When using ajustAllFonts(), try to set the fixed width/Monospace font
from the font family the user has selected, otherwise fallback to whatever
Depends on D27785