Allow custom wxDataViewCtrl renderers to easily use attributes.

Set up the DC passed to wxDataViewCustomRenderer::Render() to use the font and
colour defined by the item attribute by default so that any calls to
RenderText() from it will use them automatically.

Also added public wxDataViewCustomRenderer::GetAttr() to allow retrieving the
attribute explicitly in Render().

The column using custom renderer in the dataview sample now works as expected
in the generic version; the native ones will be corrected in the upcoming
commits.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@62590 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/gtk/dvrenderers.h

@@ -100,15 +100,15 @@ public:
     virtual ~wxDataViewCustomRenderer();
 
 
-    virtual bool Render( wxRect cell, wxDC *dc, int state ) = 0;
-
-    void RenderText( const wxString &text, int xoffset,  wxRect cell, wxDC *dc, int state );
-
-    virtual wxSize GetSize() const = 0;
-
     // Create DC on request
     virtual wxDC *GetDC();
 
+    // override the base class function to use GTK text cell renderer
+    virtual void RenderText(const wxString& text,
+                            int xoffset,
+                            wxRect cell,
+                            wxDC *dc,
+                            int state);
 
 protected: