Expose instance parameters of class methods

[realh]

Class methods have an instance parameter which needs to be exposed. Gjs accepts a GType, an object instance or a constructor for these.

[realh]

Oops, only the last commit should belong to this PR, the others are for #30.

[JumpLink]

Also tested locally and also looks good.
Here is an example how the class "ContainerClass" in @types/Gjs/Gtk-3.0.d.ts looks like with these changes:

export abstract class ContainerClass {
    /* Fields of Gtk.ContainerClass */
    parent_class: WidgetClass
    add: (container: Container, widget: Widget) => void
    remove: (container: Container, widget: Widget) => void
    check_resize: (container: Container) => void
    forall: (container: Container, include_internals: boolean, callback: Callback) => void
    set_focus_child: (container: Container, child?: Widget | null) => void
    child_type: (container: Container) => GObject.Type
    composite_name: (container: Container, child: Widget) => string
    set_child_property: (container: Container, child: Widget, property_id: number, value: any, pspec: GObject.ParamSpec) => void
    get_child_property: (container: Container, child: Widget, property_id: number, value: any, pspec: GObject.ParamSpec) => void
    get_path_for_child: (container: Container, child: Widget) => WidgetPath
    /* Methods of Gtk.ContainerClass */
    find_child_property(cclass: Container | Function | GObject.Type, property_name: string): GObject.ParamSpec | null
    handle_border_width(klass: Container | Function | GObject.Type): void
    install_child_properties(cclass: Container | Function | GObject.Type, pspecs: GObject.ParamSpec[]): void
    install_child_property(cclass: Container | Function | GObject.Type, property_id: number, pspec: GObject.ParamSpec): void
    list_child_properties(cclass: Container | Function | GObject.Type): GObject.ParamSpec[]
    static name: string
}