Add RPC xAOD PRD

Opening this now to get early comments.

I do not claim this class is complete - probably we need to add more data to it. But adding some more aux variables is relatively easy once all the "plumbing" is done, which is what I'm concentrating on here.

One obvious thing I need to resolve is

IdentifierHash RpcStrip_v1::measurementHash() const {
    // return MuonGMR4::RpcReadoutElement::measurementHash(Identifier(static_cast<Identifier::value_type>(identifier()))); 
    //FIXME! Not optimal, but in any case it doesn't work since we need to have a RRE instantiated to get the hash
    return IdentifierHash();
}

The problem here is MuonGMR4::RpcReadoutElement only takes an identifier: https://gitlab.cern.ch/atlas/athena/-/blob/main/MuonSpectrometer/MuonPhaseII/MuonDetDescr/MuonReadoutGeometryR4/MuonReadoutGeometryR4/RpcReadoutElement.h#L106

whilst e.g. MdtReadoutElement has a static second function taking layer and tube. https://gitlab.cern.ch/atlas/athena/-/blob/main/MuonSpectrometer/MuonPhaseII/MuonDetDescr/MuonReadoutGeometryR4/MuonReadoutGeometryR4/MdtReadoutElement.h#L82

(This might need changes to MuonReadoutGeometryR4)

cc @ncalace @pagessin @jojungge

ATLASRECTS-7674