Add wxDataViewCtrl::{Set,Get}CurrentItem().

Current item is the same as the selected item in single selection mode but in
multiple selection mode there was no way to neither get this item nor change
it before so add the new functions to allow doing this now.

The new methods are implemented for the generic, GTK and OS X/Cocoa versions
but only stubs are provided for OS X/Carbon.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@65228 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/osx/dataview_osx.cpp

@@ -496,6 +496,16 @@ unsigned int wxDataViewCtrl::GetCount() const
   return GetDataViewPeer()->GetCount();
 }
 
+wxDataViewItem wxDataViewCtrl::DoGetCurrentItem() const
+{
+    return GetDataViewPeer()->GetCurrentItem();
+}
+
+void wxDataViewCtrl::DoSetCurrentItem(const wxDataViewItem& item)
+{
+    GetDataViewPeer()->SetCurrentItem(item);
+}
+
 wxRect wxDataViewCtrl::GetItemRect(wxDataViewItem const& item, wxDataViewColumn const* columnPtr) const
 {
   if (item.IsOk() && (columnPtr != NULL))