Updeate PcgRSFast's setSeed method to comply with other usages

[KilianB]

PcgRSFast's setSeed should overwrite and deprecate setSeed inherited from Random the same way the other PcgInstances are doing it.
setSeed should set the seed and streamnumber accordingly to not confuse users

[KilianB]

Additionally setSeed should be defined in the pcg interface. This does not change any implementation as the subclasses already implement the method but allows the signature to be visible on Pcg references.