…ental usage of forever unstable things

fix tidy

remove dir

We weren't accounting for the case where `break` was immediately within
the `loop` block.

Split out the stable part of smir into its own crate to prevent accidental usage of forever unstable things

Some groundwork for being able to work on rust-lang/project-stable-mir#27 at all

r? `@spastorino`

Anonymize binders for `refining_impl_trait` check

We're naively using the equality impl for `ty::Clause` in the refinement check, which is okay *except* for binders, which carry some information about where they come from in the AST. Those locations are not gonna be equal between traits and impls, so anonymize those clauses so that this doesn't matter.

Fixes rust-lang#116135

…-async-function-in-main, r=wesleywiser

Add test for `const async fn`

This adds a test for rust-lang#102796

…rrors

Add context to `let: Ty = loop { break };`

We weren't accounting for the case where `break` was immediately within the `loop` block.