Suggest Rust 2018 on `<expr>.await` with no such field

When type checking a field projection (`fn check_field`) to `<expr>.await` where `<expr>: τ` and `τ` is not a primitive type, suggest switching to Rust 2018. E.g.

```
error[E0609]: no field `await` on type `std::pin::Pin<&mut dyn std::future::Future<Output = ()>>`
  --> $DIR/suggest-switching-edition-on-await.rs:31:7
   |
LL |     x.await;
   |       ^^^^^ unknown field
   |
   = note: to `.await` a `Future`, switch to Rust 2018
   = help: set `edition = "2018"` in `Cargo.toml`
   = note: for more on editions, read https://doc.rust-lang.org/edition-guide
```

Fixes rust-lang#63533

This PR also performs some preparatory cleanups in `fn check_field`; the last 2 commits are where the suggestion is introduced and tested respectively.

r? @varkor

Suggest Rust 2018 on `<expr>.await` with no such field

When type checking a field projection (`fn check_field`) to `<expr>.await` where `<expr>: τ` and `τ` is not a primitive type, suggest switching to Rust 2018. E.g.

```
error[E0609]: no field `await` on type `std::pin::Pin<&mut dyn std::future::Future<Output = ()>>`
  --> $DIR/suggest-switching-edition-on-await.rs:31:7
   |
LL |     x.await;
   |       ^^^^^ unknown field
   |
   = note: to `.await` a `Future`, switch to Rust 2018
   = help: set `edition = "2018"` in `Cargo.toml`
   = note: for more on editions, read https://doc.rust-lang.org/edition-guide
```

Fixes rust-lang#63533

This PR also performs some preparatory cleanups in `fn check_field`; the last 2 commits are where the suggestion is introduced and tested respectively.

r? @varkor

Suggest Rust 2018 on `<expr>.await` with no such field

When type checking a field projection (`fn check_field`) to `<expr>.await` where `<expr>: τ` and `τ` is not a primitive type, suggest switching to Rust 2018. E.g.

```
error[E0609]: no field `await` on type `std::pin::Pin<&mut dyn std::future::Future<Output = ()>>`
  --> $DIR/suggest-switching-edition-on-await.rs:31:7
   |
LL |     x.await;
   |       ^^^^^ unknown field
   |
   = note: to `.await` a `Future`, switch to Rust 2018
   = help: set `edition = "2018"` in `Cargo.toml`
   = note: for more on editions, read https://doc.rust-lang.org/edition-guide
```

Fixes rust-lang#63533

This PR also performs some preparatory cleanups in `fn check_field`; the last 2 commits are where the suggestion is introduced and tested respectively.

r? @varkor

Suggest Rust 2018 on `<expr>.await` with no such field

When type checking a field projection (`fn check_field`) to `<expr>.await` where `<expr>: τ` and `τ` is not a primitive type, suggest switching to Rust 2018. E.g.

```
error[E0609]: no field `await` on type `std::pin::Pin<&mut dyn std::future::Future<Output = ()>>`
  --> $DIR/suggest-switching-edition-on-await.rs:31:7
   |
LL |     x.await;
   |       ^^^^^ unknown field
   |
   = note: to `.await` a `Future`, switch to Rust 2018
   = help: set `edition = "2018"` in `Cargo.toml`
   = note: for more on editions, read https://doc.rust-lang.org/edition-guide
```

Fixes rust-lang#63533

This PR also performs some preparatory cleanups in `fn check_field`; the last 2 commits are where the suggestion is introduced and tested respectively.

r? @varkor

Rollup of 5 pull requests

Successful merges:

 - #63173 (Use libunwind from llvm-project submodule for musl targets)
 - #63462 (Opaque builtin derive macros)
 - #63539 (Suggest Rust 2018 on `<expr>.await` with no such field)
 - #63545 (Feature gate 'yield $expr?' pre-expansion)
 - #63584 (libcore: more cleanups using `#![feature(associated_type_bounds)]`)

Failed merges:

r? @ghost

Suggest Rust 2018 on `<expr>.await` with no such field

When type checking a field projection (`fn check_field`) to `<expr>.await` where `<expr>: τ` and `τ` is not a primitive type, suggest switching to Rust 2018. E.g.

```
error[E0609]: no field `await` on type `std::pin::Pin<&mut dyn std::future::Future<Output = ()>>`
  --> $DIR/suggest-switching-edition-on-await.rs:31:7
   |
LL |     x.await;
   |       ^^^^^ unknown field
   |
   = note: to `.await` a `Future`, switch to Rust 2018
   = help: set `edition = "2018"` in `Cargo.toml`
   = note: for more on editions, read https://doc.rust-lang.org/edition-guide
```

Fixes rust-lang#63533

This PR also performs some preparatory cleanups in `fn check_field`; the last 2 commits are where the suggestion is introduced and tested respectively.

r? @varkor

Suggest Rust 2018 on `<expr>.await` with no such field

When type checking a field projection (`fn check_field`) to `<expr>.await` where `<expr>: τ` and `τ` is not a primitive type, suggest switching to Rust 2018. E.g.

```
error[E0609]: no field `await` on type `std::pin::Pin<&mut dyn std::future::Future<Output = ()>>`
  --> $DIR/suggest-switching-edition-on-await.rs:31:7
   |
LL |     x.await;
   |       ^^^^^ unknown field
   |
   = note: to `.await` a `Future`, switch to Rust 2018
   = help: set `edition = "2018"` in `Cargo.toml`
   = note: for more on editions, read https://doc.rust-lang.org/edition-guide
```

Fixes rust-lang#63533

This PR also performs some preparatory cleanups in `fn check_field`; the last 2 commits are where the suggestion is introduced and tested respectively.

r? @varkor

Suggest Rust 2018 on `<expr>.await` with no such field

When type checking a field projection (`fn check_field`) to `<expr>.await` where `<expr>: τ` and `τ` is not a primitive type, suggest switching to Rust 2018. E.g.

```
error[E0609]: no field `await` on type `std::pin::Pin<&mut dyn std::future::Future<Output = ()>>`
  --> $DIR/suggest-switching-edition-on-await.rs:31:7
   |
LL |     x.await;
   |       ^^^^^ unknown field
   |
   = note: to `.await` a `Future`, switch to Rust 2018
   = help: set `edition = "2018"` in `Cargo.toml`
   = note: for more on editions, read https://doc.rust-lang.org/edition-guide
```

Fixes rust-lang#63533

This PR also performs some preparatory cleanups in `fn check_field`; the last 2 commits are where the suggestion is introduced and tested respectively.

r? @varkor

Suggest Rust 2018 on `<expr>.await` with no such field

When type checking a field projection (`fn check_field`) to `<expr>.await` where `<expr>: τ` and `τ` is not a primitive type, suggest switching to Rust 2018. E.g.

```
error[E0609]: no field `await` on type `std::pin::Pin<&mut dyn std::future::Future<Output = ()>>`
  --> $DIR/suggest-switching-edition-on-await.rs:31:7
   |
LL |     x.await;
   |       ^^^^^ unknown field
   |
   = note: to `.await` a `Future`, switch to Rust 2018
   = help: set `edition = "2018"` in `Cargo.toml`
   = note: for more on editions, read https://doc.rust-lang.org/edition-guide
```

Fixes rust-lang#63533

This PR also performs some preparatory cleanups in `fn check_field`; the last 2 commits are where the suggestion is introduced and tested respectively.

r? @varkor

Rollup of 7 pull requests

Successful merges:

 - #62593 (Group all ABI tests.)
 - #63173 (Use libunwind from llvm-project submodule for musl targets)
 - #63535 (Continue refactoring resolve and hygiene)
 - #63539 (Suggest Rust 2018 on `<expr>.await` with no such field)
 - #63584 (libcore: more cleanups using `#![feature(associated_type_bounds)]`)
 - #63612 (Do not suggest `try_into` for base types inside of macro expansions)
 - #63615 (Fix typo in DoubleEndedIterator::nth_back doc)

Failed merges:

r? @ghost