Support for records with record-type fields

[cameronwhite]

I noticed that Gsk.ColorStop is missing its color field which is a Gdk.RGBA type (https://docs.gtk.org/gsk4/struct.ColorStop.html)
From the build log:

Did not render typed record ColorStop field color: Public field "color" of type GirModel.AnyType: GirModel.Type: Gdk.RGBA can not be rendered

This isn't super high priority, and just noticed this while experimenting with porting a custom widget from Cairo (Gtk.DrawingArea) to GSK (e.g. https://docs.gtk.org/gtk4/method.Snapshot.append_linear_gradient.html)