Assembly: Implement Bill Of Materials (#14198)

* Assembly: Implementation of BOM

* Assembly: BOM: make it possible for BOM to be made without an assembly.

src/Mod/Assembly/App/BomGroup.cpp

@@ -0,0 +1,55 @@
+// SPDX-License-Identifier: LGPL-2.1-or-later
+/****************************************************************************
+ *                                                                          *
+ *   Copyright (c) 2023 Ondsel <development@ondsel.com>                     *
+ *                                                                          *
+ *   This file is part of FreeCAD.                                          *
+ *                                                                          *
+ *   FreeCAD is free software: you can redistribute it and/or modify it     *
+ *   under the terms of the GNU Lesser General Public License as            *
+ *   published by the Free Software Foundation, either version 2.1 of the   *
+ *   License, or (at your option) any later version.                        *
+ *                                                                          *
+ *   FreeCAD is distributed in the hope that it will be useful, but         *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of             *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU       *
+ *   Lesser General Public License for more details.                        *
+ *                                                                          *
+ *   You should have received a copy of the GNU Lesser General Public       *
+ *   License along with FreeCAD. If not, see                                *
+ *   <https://www.gnu.org/licenses/>.                                       *
+ *                                                                          *
+ ***************************************************************************/
+
+#include "PreCompiled.h"
+#ifndef _PreComp_
+#endif
+
+#include <App/Application.h>
+#include <App/Document.h>
+#include <App/FeaturePythonPyImp.h>
+#include <App/PropertyPythonObject.h>
+#include <Base/Console.h>
+#include <Base/Tools.h>
+
+#include "BomGroup.h"
+#include "BomGroupPy.h"
+
+using namespace Assembly;
+
+
+PROPERTY_SOURCE(Assembly::BomGroup, App::DocumentObjectGroup)
+
+BomGroup::BomGroup()
+{}
+
+BomGroup::~BomGroup() = default;
+
+PyObject* BomGroup::getPyObject()
+{
+    if (PythonObject.is(Py::_None())) {
+        // ref counter is set to 1
+        PythonObject = Py::Object(new BomGroupPy(this), true);
+    }
+    return Py::new_reference_to(PythonObject);
+}