[Macros] Accessing the "parent context" of a syntax node passed to a macro

[erneestoc (Ernesto)]

@Douglas_Gregor

this information isn't readily available in the macro process

Would this work for what I'm asking here?

Can swift macro create separate implementation of a declaration?

I'm willing to put the effort. I'd love to have a tool like mockingbird or swiftymocky but without needing a separate codegen tool. On the example above, if protocol inherited from other protocol, would we have a way to check the members of the protocol is inheriting from?