Replaces the widget packed into the tooltip with custom_widget
.
custom_widget
does not get destroyed when the tooltip goes away. By default a box with a `GtkImage` and `GtkLabel` is
embedded in the tooltip, which can be configured using set_markup and
set_icon.
this |
a `GtkTooltip` |
custom_widget |
a `GtkWidget`, or null to unset the old custom widget. |