Converts bin_window coordinates to coordinates for the tree (the full scrollable area of the tree).
Use [class@Gtk.ListView] or [class@Gtk.ColumnView] instead
| this |
a `GtkTreeView` |
| bx |
X coordinate relative to bin_window |
| by |
Y coordinate relative to bin_window |
| tx |
return location for tree X coordinate |
| ty |
return location for tree Y coordinate |