Add enums required for GObject >=3.51.0

[FakeMichau]

Not sure if that's the best approach or if it maybe should be implemented somewhere else.
Took the enums from gtk-layer-shell.
It works and in the worst case I hope this saves the maintainers some time diagnosing the cause

ref: https://gitlab.gnome.org/GNOME/pygobject/-/blob/main/docs/guide/api/flags_enums.rst

[its-darsh]

Indeed that's the right way of fixing this issue, however, this is more of a PyGObject issue with the binding, PyGObject should automatically detect what is an enum and what's not...

I had multiple plans of fixing this issue however I took the easiest route and that is waiting till upstream is fixed. I also thought about editing the implementation of Property.

[FakeMichau]

Are they aware of the issue? I looked at issues on gnome's gitlab for gobject-introspection but can't tell if any of them relate to this.