[Gui] move xerces to precompiled header

as suggested here: https://github.com/FreeCAD/FreeCAD/commit/0235a172#r68066840

src/Gui/ApplicationPy.cpp

@@ -20,7 +20,6 @@
  *                                                                         *
  ***************************************************************************/
 
-
 #include "PreCompiled.h"
 
 #ifndef _PreComp_
@@ -31,20 +30,18 @@
 # include <Inventor/SoInput.h>
 # include <Inventor/actions/SoGetPrimitiveCountAction.h>
 # include <Inventor/nodes/SoSeparator.h>
+# include <xercesc/util/TranscodingException.hpp>
+# include <xercesc/util/XMLString.hpp>
 #endif
 
 #include <boost/regex.hpp>
-#include <CXX/Objects.hxx>
-#include <Inventor/MarkerBitmaps.h>
-#include <xercesc/util/TranscodingException.hpp>
-#include <xercesc/util/XMLString.hpp>
 
 #include <App/DocumentObjectPy.h>
 #include <App/DocumentPy.h>
 #include <App/PropertyFile.h>
 #include <Base/Interpreter.h>
 #include <Base/Console.h>
-#include <Language/Translator.h>
+#include <CXX/Objects.hxx>
 
 #include "Application.h"
 #include "BitmapFactory.h"
@@ -67,6 +64,8 @@
 #include "WidgetFactory.h"
 #include "Workbench.h"
 #include "WorkbenchManager.h"
+#include "Inventor/MarkerBitmaps.h"
+#include "Language/Translator.h"
 
 
 using namespace Gui;