Gui: add virtual method containsViewProvider to MDIView and re-implement it in some sub-classes

Improve Document::setActiveView to not always switch to the first 3D view but check the currently active view before

src/Gui/View3DInventor.cpp

@@ -84,6 +84,7 @@
 #include <Inventor/nodes/SoOrthographicCamera.h>
 
 #include "View3DInventorExamples.h"
+#include "ViewProviderDocumentObject.h"
 #include "SoFCSelectionAction.h"
 #include "View3DPy.h"
 #include "SoFCDB.h"
@@ -516,6 +517,11 @@ void View3DInventor::print(QPrinter* printer)
     p.end();
 }
 
+bool View3DInventor::containsViewProvider(const ViewProvider* vp) const
+{
+    return _viewer->containsViewProvider(vp);
+}
+
 // **********************************************************************************
 
 bool View3DInventor::onMsg(const char* pMsg, const char** ppReturn)