Allow specifying multiple formats to be accepted when dragging data to
wxDataViewCtrl in the generic and Cocoa implementations.
Add wxDataViewCtrlBase::EnableDropTarget() overload taking an array of
wxDataFormats to support this at the API level.
Add new DoEnableDropTarget() used by both EnableDropTarget() overloads
and implement it in the generic and Cocoa ports. GTK implementation
still uses only a single format, as before.
Also refactor the Cocoa implementation: all operations using dragged
data are now handled by wxDropTarget and unnecessary DataViewPboardType
as removed.
Update the dataview sample to show the new functionality.
7129d2b11c