Adds a window to `application`.
This call can only happen after the `application` has started; typically, you should add new application windows in response to the
emission of the `GApplication:GtkApplication:activate` signal.
This call is equivalent to setting the [[email protected]:application] property of `window` to `application`.
Normally, the connection between the application and the window will remain until the window is destroyed, but you can explicitly remove it with [[email protected]_window].
GTK will keep the `application` running as long as it has any windows.
| this |
a `GtkApplication` |
| window |
a `GtkWindow` |