getDesktopPrefixes

auto currentDesktopGuard = EnvGuard("XDG_CURRENT_DESKTOP", "LXQT");
assert(equal(getDesktopPrefixes(), ["lxqt"]));

environment["XDG_CURRENT_DESKTOP"] = "unity:GNOME";
assert(equal(getDesktopPrefixes(), ["unity", "gnome"]));