Gui: Add SplitButton widget

This adds SplitButton widget that has one primary action and possibly
more secondary ones accessible via menu.

src/Gui/SplitButton.h

@@ -0,0 +1,69 @@
+// SPDX-License-Identifier: LGPL-2.1-or-later
+/****************************************************************************
+ *                                                                          *
+ *   Copyright (c) 2025 Kacper Donat <kacper@kadet.net>                     *
+ *                                                                          *
+ *   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/>.                                       *
+ *                                                                          *
+ ***************************************************************************/
+
+#ifndef FREECAD_FCSPLITBUTTON_H
+#define FREECAD_FCSPLITBUTTON_H
+
+#include <QWidget>
+#include <QPushButton>
+#include <QToolButton>
+#include <QMenu>
+
+namespace Gui
+{
+
+class SplitButton: public QWidget
+{
+    Q_OBJECT
+public:
+    explicit SplitButton(QWidget* parent = nullptr);
+    explicit SplitButton(const QString& text, QWidget* parent = nullptr);
+
+    QPushButton* mainButton() const
+    {
+        return m_main;
+    }
+
+    QToolButton* menuButton() const
+    {
+        return m_menuButton;
+    }
+
+    QMenu* menu() const
+    {
+        return m_menu;
+    }
+
+Q_SIGNALS:
+    void defaultClicked();
+    void triggered(QAction*);
+
+private:
+    QPushButton* m_main;
+    QToolButton* m_menuButton;
+    QMenu* m_menu;
+};
+
+}  // namespace Gui
+
+#endif  // FREECAD_FCSPLITBUTTON_H