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.

since freebsd 11 had been removed, minimum is now 12.

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.

If we encounter a borrow error on `vec![1, 2, 3].iter()`, suggest
`into_iter`.

Fix rust-lang#68445.

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.

…gnatures

std: freebsd build update.

since freebsd 11 had been removed, minimum is now 12.

Suggest relaxing implicit `type Assoc: Sized;` bound

Fix rust-lang#85378.

coverage: Simplify the injection of coverage statements

This is a follow-up to rust-lang#116046 that I left out of that PR because I didn't want to make it any larger.

After the various changes we've made to how coverage data is stored and transferred, the old code structure for injecting coverage statements into MIR is built around a lot of constraints that don't exist any more. We can simplify it by replacing it with a handful of loops over the BCB node/edge counters and the BCB spans.

---

`@rustbot` label +A-code-coverage

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```

…k,cjgillot

coverage: Fix inconsistent handling of function signature spans

While doing some more cleanup of `spans`, I noticed a strange inconsistency in how function signatures are handled. Normally the function signature span is treated as though it were executable as part of the start of the function, but in some cases the signature span disappears entirely from coverage, for no obvious reason.

This is caused by the fact that spans created by `CoverageSpan::for_fn_sig` don't add the span to their `merged_spans` field (unlike normal statement/terminator spans). In cases where the span-processing code looks at those merged spans, it thinks the signature span is no longer visible and deletes it.

Adding the signature span to `merged_spans` resolves the inconsistency.

(Prior to rust-lang#116409 this wouldn't have been possible, because there was no case in the old `CoverageStatement` enum representing a signature. Now that `merged_spans` is just a list of spans, that's no longer an obstacle.)

Mention `into_iter` on borrow errors suggestions when appropriate

If we encounter a borrow error on `vec![1, 2, 3].iter()`, suggest `into_iter`.

Fix rust-lang#68445.

…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.