TD: [skip ci] activate PCH of TechDraw (Gui) and use forward declarations

For MSVC this reduces compile time by ~20%

src/Mod/TechDraw/Gui/SymbolChooser.cpp

@@ -21,6 +21,7 @@
  ***************************************************************************/
 
 #include "PreCompiled.h"
+#include <QListWidget>
 
 #include <App/Application.h>
 #include <Mod/TechDraw/Gui/ui_SymbolChooser.h>
@@ -48,6 +49,10 @@ SymbolChooser::SymbolChooser(QWidget *parent,
     setUiPrimary();
 }
 
+SymbolChooser::~SymbolChooser()
+{
+}
+
 void SymbolChooser::setUiPrimary()
 {
     // Base::Console().Message("SC::setUiPrimary()\n");