Base: Add Base::ProgressIndicator for OCCT progress reporting

Introduce a new `ProgressIndicator` base class
(`ProgressIndicator.h`/`.cpp`) with a singleton-managed, no-op default
implementation matching OCCT’s `Message_ProgressIndicator` interface.
Update `CMakeLists.txt` to include the new sources.

src/Base/ProgressIndicator.cpp

@@ -0,0 +1,33 @@
+// SPDX-License-Identifier: LGPL-2.1-or-later
+/***************************************************************************
+ *   Copyright (c) 2025 James Stanley <james@incoherency.co.uk>            *
+ *                                                                         *
+ *   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 "ProgressIndicator.h"
+
+namespace Base
+{
+
+ProgressIndicator::ProgressIndicator() = default;
+ProgressIndicator::ProgressIndicator(const ProgressIndicator&) = default;
+ProgressIndicator& ProgressIndicator::operator=(const ProgressIndicator&) = default;
+ProgressIndicator::~ProgressIndicator() = default;
+
+}  // namespace Base