C++: Introduce caches to Clone* classes

Done-with: Erik Verbruggen <erik.verbruggen@digia.com>
Task-number: QTCREATORBUG-8747

Change-Id: I7cb694f8180c6aa932b07066d98d095340111324
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>
Reviewed-by: xSacha
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: Eike Ziller <eike.ziller@digia.com>