Utils: Promote CppEditor::StringTable

It's useful on a more general level, and it's only useful as
real singleton.

Change-Id: I1da38a8eb6f9332a36261288d1b088ca6204eb7a
Reviewed-by: Jarek Kobus <jaroslaw.kobus@qt.io>

src/libs/utils/stringtable.h

@@ -0,0 +1,13 @@
+// Copyright (C) 2016 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0+ OR GPL-3.0 WITH Qt-GPL-exception-1.0
+
+#pragma once
+
+#include <utils/utils_global.h>
+
+namespace Utils::StringTable {
+
+QTCREATOR_UTILS_EXPORT QString insert(const QString &string);
+QTCREATOR_UTILS_EXPORT void scheduleGC();
+
+} // Utils::StringTable