Sets the pixel size to use for named icons.
If the pixel size is set to a value != -1, it is used instead of the icon size set by [method@Gtk.Image.set_from_icon_name].
the new pixel size
See Implementation
Sets the pixel size to use for named icons.
If the pixel size is set to a value != -1, it is used instead of the icon size set by [method@Gtk.Image.set_from_icon_name].