Sketcher: Fix crash on constraint rename

========================================

Report:
https://github.com/FreeCAD/FreeCAD/pull/4183
https://github.com/realthunder/FreeCAD_assembly3/issues/387

Problem:
renameConstraint() previously implemented exclusively in SketchObjectPyImp.cpp,
will change the Constraints property without updating the solver. A prospective
drag operation would rely on a deleted pointer constraint which leads to the
crash.

Solution:
- mark the solver status as needing an update
- leverage new through sketchobject r/w interface to ensure solver is synchronised
before the temporary move operation starts

Bonus:
move the core of the function to SketchObject.cpp so that input data validity
check on constraint change is inhibited.

src/Mod/Sketcher/App/SketchObjectPyImp.cpp

@@ -417,14 +417,8 @@ PyObject* SketchObjectPy::renameConstraint(PyObject *args)
         }
     }
 
-    // only change the constraint item if the names are different
-    const Constraint* item = this->getSketchObjectPtr()->Constraints[Index];
-    if (item->Name != Name) {
-        Constraint* copy = item->clone();
-        copy->Name = Name;
-        this->getSketchObjectPtr()->Constraints.set1Value(Index, copy);
-        delete copy;
-    }
+    this->getSketchObjectPtr()->renameConstraint(Index, Name);
+
     Py_Return;
 }