Replace statically bound GLib.Variant.new_tuple() with GI

Remove the static implementation of _wrap_pyg_variant_new_tuple with
usage of the dynamic version coming from GI. Array marshalling has
drastically improved in recent years making the dynamic version usable
with a small compatibility shim for the arguments.

https://bugzilla.gnome.org/show_bug.cgi?id=735199
Fix crash in GList/GSList marshaling error handling path.

In case PySequence_GetItem() failed, the retured NULL was passed to PyDECREF.

https://bugzilla.gnome.org/show_bug.cgi?id=735201