Use vector instead of array of wxDataFormats

Also rename EnableDropTarget() to EnableDropTargets(), as calling
EnableDropTarget(wxDF_XXX) would be ambiguous due to the existence of a
non-explicit wxVector ctor taking size_t (which is a mistake on its own,
but is probably not worth changing any more).

src/generic/datavgen.cpp

@@ -5801,7 +5801,7 @@ bool wxDataViewCtrl::EnableDragSource( const wxDataFormat &format )
     return m_clientArea->EnableDragSource( format );
 }
 
-bool wxDataViewCtrl::DoEnableDropTarget( const wxDataFormatArray &formats )
+bool wxDataViewCtrl::DoEnableDropTarget( const wxVector<wxDataFormat> &formats )
 {
     wxDataViewDropTarget* dt = NULL;
     if (wxDataObject* dataObject = CreateDataObject(formats))