Adding symbols for protocol conformance’s code generation

We should have some symbol to explicitly say that the protocol conformance’s implementation is to be generated by compiler (e.g. Codable, Hashable, Equatable).
Some declarations can be hard to see if it matchs the protocol due to typos.
It would also make the intend clearer if programmers are rolling their own implementations.

I’m thinking something along the line of

class foo: @autogenerate(Codable) {

All discussions for previous proposal are available for your review on this site. You'll see that having an explicit marker of synthesized conformance was put forward and rejected after thorough deliberation and review.