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

For MSVC this reduces compile time by ~20%

src/Mod/TechDraw/Gui/ViewProviderViewSection.cpp

@@ -41,6 +41,7 @@
 
 #include "TaskSectionView.h"
 #include "ViewProviderViewSection.h"
+#include "QGIView.h"
 
 using namespace TechDrawGui;