Add the possibility to disable invisible wxDataViewCtrl items.

Add new wxDataViewModel::IsEnabled() and wxDataViewListStore::IsEnabledByRow()
methods and implement support for actually disabling the items in wxOSX/Cocoa
native implementation of wxDataViewCtrl and limited support for it in the
generic version.

We need to implement this in wxGTK using GtkCellRenderer "sensitive" propriety
later.

Closes #12686.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66403 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/osx/dvrenderer.h

@@ -87,6 +87,9 @@ public:
     // called to ensure that the given attribute will be used for rendering the
     // next cell (which had been already associated with this renderer before)
     virtual void OSXApplyAttr(const wxDataViewItemAttr& attr);
+
+    // called to set the state of the next cell to be rendered
+    virtual void OSXApplyEnabled(bool enabled);
 #endif // Cocoa
 
 private: