One saved waveform: a component named by the LABELS of the custom component instances entered to reach it, then its own label, and which of its ports. Not ids and not array indices, because this is written to a file and read back against a design that has been edited since. See `WavePath.fs`, which resolves it both ways. The field names are prefixed because F# resolves an unannotated record field to the last type declaring it, and `PortType`/`PortNumber` are `WaveIndexT`'s.