Utils: Move forward declaration of SmallString in an extra header

Change-Id: I6da1cc60d425f654a31570373eb3b4f660d5f975
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/libs/utils/smallstringfwd.h

@@ -0,0 +1,37 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+
+#pragma once
+
+namespace Utils {
+
+using uint = unsigned int;
+
+template <uint Size>
+class BasicSmallString;
+using SmallString = BasicSmallString<31>;
+using PathString = BasicSmallString<190>;
+
+} // namespace Utils