Sets tooltip as the contents of the tooltip for the icon at the specified position.
tooltip is assumed to be marked up with Pango Markup.
Use null for tooltip to remove an existing tooltip.
See also [[email protected]_tooltip_markup] and [[email protected]_icon_tooltip_text].
| this |
a `GtkEntry` |
| icon_pos |
the icon position |
| tooltip |
the contents of the tooltip for the icon |