Uplift the (new solver) canonicalizer into `rustc_next_trait_solver`
Uplifts the new trait solver's canonicalizer into a new crate called `rustc_next_trait_solver`.
The crate name is literally a bikeshed-avoidance name, so let's not block this PR on that -- renames are welcome later.
There are a host of other changes that were required to make this possible:
* Expose a `ConstTy` trait to get the `Interner::Ty` from a `Interner::Const`.
* Expose some constructor methods to construct `Bound` variants. These are currently methods defined on the interner themselves, but they could be pulled into traits later.
* Expose a `IntoKind` trait to turn a `Ty`/`Const`/`Region` into their corresponding `*Kind`s.
* Some minor tweaks to other APIs in `rustc_type_ir`.
The canonicalizer code itself is best reviewed **with whitespace ignored.**
r? ``@lcnr``
Move EagerResolution to rustc_infer::infer::resolve
`EagerResolver` fits better in `rustc_infer::infer::resolver`.
Started to disentagle #118118 that has a lot of unrelated things.
r? `@compiler-errors` `@lcnr`
EvalCtxt::commit_if_ok don't inherit nested goals
we use it to check whether an alias is rigid, so we want to avoid considering an alias rigid simply because the inference constraints from normalizing it caused another nested goal fail
r? `@compiler-errors`
Remove `PredicateKind::ClosureKind`
We don't need the `ClosureKind` predicate kind -- instead, `Fn`-family trait goals are left as ambiguous, and we only need to make progress on `FnOnce` projection goals for inference purposes.
This is similar to how we do confirmation of `Fn`-family trait and projection goals in the new trait solver, which also doesn't use the `ClosureKind` predicate.
Some hacky logic is added in the second commit so that we can keep the error messages the same.
new solver normalization improvements
cool beans
At the core of this PR is a `try_normalize_ty` which stops for rigid aliases by using `commit_if_ok`.
Reworks alias-relate to fully normalize both the lhs and rhs and then equate the resulting rigid (or inference) types. This fixes https://github.com/rust-lang/trait-system-refactor-initiative/issues/68 by avoiding the exponential blowup. Also supersedes #116369 by only defining opaque types if the hidden type is rigid.
I removed the stability check in `EvalCtxt::evaluate_goal` due to https://github.com/rust-lang/trait-system-refactor-initiative/issues/75. While I personally have opinions on how to fix it, that still requires further t-types/`@nikomatsakis` buy-in, so I removed that for now. Once we've decided on our approach there, we can revert this commit.
r? `@compiler-errors`
Fix depth check in ProofTreeVisitor.
The hack to cutoff overflows and cycles in the new trait solver was incorrect. We want to inspect everything with depth [0..10].
This fix exposed a previously unseen bug, which caused the compiler to ICE when invoking `trait_ref` on a non-assoc type projection. I simply added the guard in the `AmbiguityCausesVisitor`, and updated the expected output for the `auto-trait-coherence` test which now includes the extra note:
```text
|
= note: upstream crates may add a new impl of trait `std::marker::Send` for type `OpaqueType` in future versions
```
r? `@lcnr`
