Add support for CPD regression testing

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This should add some sample projects for other languages (like C++) and also use the projects we already use for PMD tests.

This will come in handy whenever we optimize the CPD algorithm to verify, we don't loose duplications or match slightly differences code parts.

• See [core] Refactor CPD internals to improve efficiency pmd#6215
• See [core] Reduce memory usage of CPD's MatchCollector pmd#6150
• See [core] CPD throws java.lang.OutOfMemoryError: Java heap space pmd#6145
• See [cpp] Repeated Duplication blocks pmd#2438