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/SketchObject.cpp

@@ -8002,6 +8002,27 @@ int SketchObject::autoRemoveRedundants(bool updategeo)
     return redundants.size();
 }
 
+int SketchObject::renameConstraint(int GeoId, std::string name)
+{
+    // only change the constraint item if the names are different
+    const Constraint* item = Constraints[GeoId];
+
+    if (item->Name != name) {
+        Base::StateLocker lock(managedoperation, true); // no need to check input data validity as this is an sketchobject managed operation.
+
+        Constraint* copy = item->clone();
+        copy->Name = name;
+
+        Constraints.set1Value(GeoId, copy);
+        delete copy;
+
+        solverNeedsUpdate = true; // make sure any prospective solver access updates the constraint pointer that just got invalidated
+
+        return 0;
+    }
+    return -1;
+}
+
 std::vector<Base::Vector3d> SketchObject::getOpenVertices(void) const
 {
     std::vector<Base::Vector3d> points;