Looks up a named icon for a desired size and window scale, returning a `GtkIconPaintable`.
The icon can then be rendered by using it as a `GdkPaintable`, or you can get information such as the filename and size.
If the available
icon_name is not available and
fallbacks are provided, they will be tried in order.
If no matching icon is found, then a paintable that renders the "missing icon" icon is returned. If you need to do something else for missing icons you need to use [method@Gtk.IconTheme.has_icon].
Note that you probably want to listen for icon theme changes and update the icon. This is usually done by overriding the GtkWidgetClass.css-changed() function.
the name of the icon to lookup
desired icon size.
the window scale this will be displayed on
text direction the icon will be displayed in
flags modifying the behavior of the icon lookup
a `GtkIconPaintable` object containing the icon.