[codegen] Opportunistically make names into the originals from the user input program

Right now in the generated pipeline you'll see names like `p1_add_42_foo`, but arguably the `add_42` is only useful to compiler engineers and could be emitted as sideband metadata that we overlay on the verilog with our own bespoke debug tooling. It seems like we could opportunistically recover names. If we wanted to be conservative about the correspondence, we could try to tag when rewrites changed nodes semantically and avoid recovering the original names in those cases.

This was somewhat spurred by the nice better names in #1028 we could get opportunistically, there's something analogous we can do for codegen I bet.