Deprecate KGlobalSettings::*Font methods in favor of QFontsDatabase::systemFont
Moves the code from KGlobalSettings to the KDE platform theme to handle
fonts properly, according to Qt setting.
Port uses of KGlobalSettings::*Fonts to newer alternatives.
Drop some MacOS switches regarding the fonts. It doesn't make sense since
on a MacOS environment, applications will be running on the MacOS QPA.
REVIEW: 111409