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/msw/headerctrl.cpp

@@ -38,6 +38,7 @@
 #include "wx/msw/wrapcctl.h"
 #include "wx/msw/private.h"
 #include "wx/msw/private/customdraw.h"
+#include "wx/msw/private/winstyle.h"
 
 #ifndef HDM_SETBITMAPMARGIN
     #define HDM_SETBITMAPMARGIN 0x1234
@@ -402,12 +403,8 @@ void wxHeaderCtrl::DoInsertItem(const wxHeaderColumn& col, unsigned int idx)
         }
     }
 
-    long controlStyle = ::GetWindowLong(GetHwnd(), GWL_STYLE);
-    if ( hasResizableColumns )
-        controlStyle &= ~HDS_NOSIZING;
-    else
-        controlStyle |= HDS_NOSIZING;
-    ::SetWindowLong(GetHwnd(), GWL_STYLE, controlStyle);
+    wxMSWWinStyleUpdater(GetHwnd())
+        .TurnOnOrOff(!hasResizableColumns, HDS_NOSIZING);
 }
 
 void wxHeaderCtrl::DoSetColumnsOrder(const wxArrayInt& order)