Add support for a 5th modifier key called "hyper",
this is a modifier supported on Wayland & X11 although
other platforms could support an additional modifier too.
Both GNOME and KDE can map CapsLock to Hyper.
Other compositors can use the XKB_DEFAULT_OPTIONS environment variable.
This allows users to have an additional modifier for their own use
that doesn't conflict with other keys.
Ref !136340
5e2b421996