.index() is dependent on the order specified in the .proto file.
Minitables create their own ordering, which represent the true index that we're interested in set_alias.
This can be fetched via .layout_index when we have a upb::FieldDefPtr.
PiperOrigin-RevId: 691825782
We unify hpb's impl to utilize Protobuf's canonical printer, as opposed to a bespoke solution.
- augment hpb::Context with EmitLegacy, which keeps the $* syntax while we convert. This allows for a far simpler transitional pathway, and we can incrementally port to .Emit() as we see fit. Of course, all new calls should use .Emit().
- use the Context to wrap io::Printer and any hpb-specific info (e.g. what backend we're using)
PiperOrigin-RevId: 686198921
Hong Shin