Fix rust-lang#85378.

The `Instance::body()` returns a monomorphized body.

For that, we had to implement visitor that monomorphize types and
constants. We are also introducing the RustcInternal trait that will
allow us to convert back from Stable to Internal.

Note that this trait is not yet visible for our users as it depends on
Tables. We should probably add a new trait that can be exposed.

When encountering a binding that isn't found but has a typo suggestion
for a binding with a leading underscore, suggest changing the binding
definition instead of the use place.

Fix rust-lang#60164.

When the number of type parameters in the associated function of an impl
and its trait differ, we now *always* point at the trait one, even if it
comes from a foreign crate. When it is local, we point at the specific
params, when it is foreign, we point at the whole associated item.

Fix rust-lang#69944.

Newcomers might get confused that `mod` is the only way of defining
scopes, and that it can be used as if it were `use`.

Fix rust-lang#69492.

Suggest relaxing implicit `type Assoc: Sized;` bound

Fix rust-lang#85378.

Typo suggestion to change bindings with leading underscore

When encountering a binding that isn't found but has a typo suggestion for a binding with a leading underscore, suggest changing the binding definition instead of the use place.

Fix rust-lang#60164.

Add stable Instance::body() and RustcInternal trait

The `Instance::body()` returns a monomorphized body.

For that, we had to implement visitor that monomorphize types and constants. We are also introducing the RustcInternal trait that will allow us to convert back from Stable to Internal.

Note that this trait is not yet visible for our users as it depends on Tables. We should probably add a new trait that can be exposed.

The tests here are very simple, and I'm planning on creating more exhaustive tests in the project-mir repo. But I was hoping to get some feedback here first.

r? ``@oli-obk``

Mention the syntax for `use` on `mod foo;` if `foo` doesn't exist

Newcomers might get confused that `mod` is the only way of defining scopes, and that it can be used as if it were `use`.

Fix rust-lang#69492.

…rrors

Point at assoc fn definition on type param divergence

When the number of type parameters in the associated function of an impl and its trait differ, we now *always* point at the trait one, even if it comes from a foreign crate. When it is local, we point at the specific params, when it is foreign, we point at the whole associated item.

Fix rust-lang#69944.