Simplify changing window styles in wxMSW code

Add wxMSWWinStyleUpdater and wxMSWWinExStyleUpdater helper classes which
allow writing code changing GWL_STYLE and GWL_EXSTYLE bits,
respectively, in a shorter and more clear way.

There should be no real changes in behaviour.

src/propgrid/manager.cpp

@@ -1508,10 +1508,8 @@ void wxPropertyGridManager::RecreateControls()
                 #define WS_EX_COMPOSITED        0x02000000L
             #endif
 
-            HWND hWnd = (HWND)m_pToolbar->GetHWND();
-
-            ::SetWindowLong( hWnd, GWL_EXSTYLE,
-                             ::GetWindowLong(hWnd, GWL_EXSTYLE) | WS_EX_COMPOSITED );
+            wxMSWWinExStyleUpdater(GetHwndOf(m_pToolbar))
+                .TurnOn(WS_EX_COMPOSITED);
             */
 
         #endif