[Xwt] Detect system fonts in ValidateObject and return a different instance in those cases.
[Xwt] Detect system fonts in ValidateObject and return a different instance in those cases.

Since system fonts are singleton instances, making them go through InitForToolkit corrupt their internal state which mean they can't be reliably used by their original toolkit anymore.

Instead, we try to detect if the font is a system one and in that case we swap instances with the equivalent system font as given by the new toolkit FontBackendHandler.

TheBrainTech/xwt,mminns/xwt,directhex/xwt,residuum/xwt,akrisiun/xwt,hamekoz/xwt,hwthomas/xwt,steffenWi/xwt,cra0zy/xwt,iainx/xwt,mminns/xwt,lytico/xwt,mono/xwt,antmicro/xwt