Sets the icon for a given drag from a named themed icon.
See the docs for IconTheme for more details. Note that the size of the icon depends on
the icon theme (the icon is loaded at the symbolic size DND), thus hot_x
and hot_y have to be used with care.
| context |
the context for a drag (This must be called with a context for the source side of a drag) |
| icon_name |
name of icon to use |
| hot_x |
the X offset of the hotspot within the icon |
| hot_y |
the Y offset of the hotspot within the icon |