Add a separate wxControlRenderer::DrawButtonLabel() too.

wxControlRenderer::DrawLabel() was used by both wxStaticText and wxButton but
their labels may need to be drawn differently and wxRenderer does have
different DrawLabel() and DrawButtonLabel() to do it. Now also add a separate
method for the buttons to wxControlRenderer.

See #11220.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@62004 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/univ/renderer.h

@@ -870,8 +870,9 @@ public:
     wxControlRenderer(wxWindow *control, wxDC& dc, wxRenderer *renderer);
 
     // operations
-    void DrawLabel(const wxBitmap& bitmap = wxNullBitmap,
-                   wxCoord marginX = 0, wxCoord marginY = 0);
+    void DrawLabel();
+    void DrawButtonLabel(const wxBitmap& bitmap = wxNullBitmap,
+                         wxCoord marginX = 0, wxCoord marginY = 0);
 #if wxUSE_LISTBOX
     void DrawItems(const wxListBox *listbox,
                    size_t itemFirst, size_t itemLast);