Modernize type names in the compiler

[jroesch]

This PR modernizes some names in the type checker. The only remaining snake_case name in ty.rs is ctxt which should be resolved by @eddyb's pending refactor. We can bike shed over the names, it would just be nice to bring the type checker inline with modern Rust.

r? @eddyb

cc @nikomatsakis

[arielb1]

TypeWithMutability seems very verbose. It is basically usefully used about three times (as the output of ty::deref, in Ty, and uselessly in Field) - I would rather remove it.

[jroesch]

@arielb1 totally okay with bike shedding or removal. I'll remove it and tack another commit on here.

[nikomatsakis]

I hate to ask for this, but I'd rather have ty::TypeError::CyclicTy (i.e., not pub use all the names from the enum)

[jroesch]

Yeah I wanted to do it, but wasn't sure how much pain it was to fix. I'll bite the bullet.

[jroesch]

would you be okay with just TypeError::Variant? I think it is slightly less verbose and just as clear.

[nikomatsakis]

lgtm

[nikomatsakis]

r=me whenever you feel you've suffered enough :)

[bkoropoff]

+1, this always tripped me up.

[jroesch]

@bors r=nikomatsakis

[bors]

📌 Commit 19218ee has been approved by nikomatsakis

[bors]

⌛ Testing commit 19218ee with merge adcae00...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt