Gets the area where entry’s icon at icon_pos is drawn.
This function is useful when drawing something to the entry in a draw callback.
If the entry is not realized or has no icon at the given position, icon_area is filled with zeros. Otherwise,
icon_area will be filled with the icon's allocation, relative to this's allocation.
| this |
A `GtkEntry` |
| icon_pos |
Icon position |
| icon_area |
Return location for the icon’s area |