Use OCCT Handle macro for Handle_ classes

This is the result of running OCCT's upgrade script provided
with OCCT 7.0. See
https://www.opencascade.com/content/freecad-occt710-and-windows-rtti-data-missing#comment-form
and
https://www.forum.freecadweb.org/viewtopic.php?f=4&t=21405&start=120#p169019
for why this is necessary for OCCT >= 7.1

src/Mod/Part/App/ProgressIndicator.cpp

@@ -34,7 +34,7 @@ using namespace Part;
   #include <Transfer_TransientProcess.hxx>
 
   STEPControl_Reader aReader;
-  Handle_Message_ProgressIndicator pi = new ProgressIndicator(100);
+  Handle(Message_ProgressIndicator) pi = new ProgressIndicator(100);
 
   pi->NewScope(20, "Loading STEP file...");
   pi->Show();