Update private rustc datastructures to match conventions

[Gankra]

Right now it's in a kind of zombie russian-roulette state where anything called "map" might want find or get, and there's no obvious way to know without looking it up or letting the compiler error out. I assume you guys aren't fans of that.

[steveklabnik]

Triage: I'm not sure if this work has been done or not.

[ahmedcharles]

Does anyone know what this means or what work needs to be done?

[Mark-Simulacrum]

I propose that this be closed, with more specific issues being opened if they're found.

[Mark-Simulacrum]

Closing. There's no specific information here to make keeping this worth it.