Make FOLDERID_Downloads available as a special location

I would like to have the download folder location made available in enum File::SpecialLocationType. This would be very convenient for allowing my customers who have downloaded a license file to find it using the FileChooser class.  FOLDERID_Downloads is an enumeration available in Windows and I would like to see it mapped to a new SpecialLocationType in JUCE.

Good request, thanks!