This allows us to simplify some of the logic, and get rid of a
`gdk_seat_grab()` which might trigger unwanted popups. It's also a bit
more future-proof, as it uses the same mechanism to what is used in
GTK4 for event handling.
While we're at it, stop storing a separate `priv` pointer, which would
allow us to use `G_DECLARE_FINAL_TYPE()` in the future.
So it works with all GObject versions, until we determine how useful
it is generally, and what API it should get for possible
libgimpwidgets inclusion.
Swallow GtkHSV back into GIMP and call it GimpColorWheel. Keep it in
modules/ for the time being. Clean up and undeprecate it. Replace
set_metrics() API by set_ring_fraction() and make it follow the size
of its parent container, making its use straightforward. Kept it clean
of GIMP color types so it can be easily adapted by e.g. Inkscape.
Niels De Graef