Utils: Introduce a TemporaryDirectory and TemporaryFile class

Both wrap the corresponding Qt class, but make sure all temporary files
or directories are created inside a "master temporary directory".

Change-Id: I55461be507c828c965224c02863ea5ed9bbf9498
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/plugins/autotest/autotestunittests.h

@@ -26,7 +26,6 @@
 #pragma once
 
 #include <QObject>
-#include <QTemporaryDir>
 
 namespace CppTools { namespace Tests { class TemporaryCopiedDir; } }