Sys.Drawing.SystemFonts does not return UI fonts being used in system

The current mono implementation of System.Drawing.SystemFonts is hard-coded to return "Microsoft Sans Serif" and "Tahoma" for system font queries. Even though this matches MSDN-documented values for Windows, this violates the intended semantics of this class, and produces surprises for cross-platform Winforms developers.

With fontconfig usage in libgdiplus, a quick and (kind of) dirty fix is to replace them with "Sans" (or "Ubuntu" if you want to.) A more MSDN-friendly solution[1] is to return GenericSansSerif directly, however this ends up pointing to libgdiplus's implementation which ends up giving MS Sans Serif too.
  [1]: https://msdn.microsoft.com/en-us/library/system.drawing.systemfonts.defaultfont(v=vs.110).aspx

A related workaround in fontconfig is to alias Microsoft Sans Serif to Helvetica in 30-metric-aliases.conf (fd.o 95232). This should at least solve the issue that fontconfig most likely knows nothing about matching "Microsoft Sans Serif".