Utils: Include from future std::span

std::span is a universal class to represent a non owning contiguous data.
You can even manipulate the data but you can not change the size like sort.
It's very nice for interfaces which call in other code but don't need to
own the container or make an internal copy anyway.

https: //en.cppreference.com/w/cpp/container/span
https: //solarianprogrammer.com/2019/11/03/cpp-20-span-tutorial/

Change-Id: Iaced1bd60c14b2fd7ea6576bb6e1720ed8990da8
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/libs/utils/span.h

@@ -0,0 +1,40 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 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
+
+#if __cplusplus >= 202002L
+#include <span>
+
+namespace Utils {
+using std::as_bytes;
+using std::as_writable_bytes;
+using std::get;
+using std::span;
+} // namespace Utils
+#else
+#define TCB_SPAN_NAMESPACE_NAME Utils
+#include <3rdparty/span/span.hpp>
+#endif