Avoid setting attributes in GTK wxDataViewRenderer if not supported.

If the native renderer doesn't support the properties which we map our
attributes to, trying to set them is useless and results in GTK+ warnings so
don't do it.

Add wxDataViewRenderer::GtkSupportsAttrs() which can be overridden to indicate
whether the renderer supports attributes or not. We probably could use
g_object_class_find_property() instead to detect it automatically but for now
these properties are all supported only by GtkCellRendererText and not
supported anywhere else so using a single virtual function seems tidier.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@62591 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/gtk/dvrenderers.h

@@ -41,6 +41,8 @@ public:
 
     virtual void SetAlignment( int align );
 
+    virtual bool GtkSupportsAttrs() const { return true; }
+
 protected:
     // implementation of Set/GetValue()
     bool SetTextValue(const wxString& str);