Add wxDataViewCtrlBase::SetAlternateRowColour()

Previously this method was only available in the generic wxDataViewCtrl,
move it to the base class to make it possible calling it in portable
code and document it.

Closes #14617.

src/generic/datavgen.cpp

@@ -5781,9 +5781,10 @@ bool wxDataViewCtrl::SetHeaderAttr(const wxItemAttr& attr)
     return true;
 }
 
-void wxDataViewCtrl::SetAlternateRowColour(const wxColour& colour)
+bool wxDataViewCtrl::SetAlternateRowColour(const wxColour& colour)
 {
     m_alternateRowColour = colour;
+    return true;
 }
 
 void wxDataViewCtrl::SelectAll()