The grouping led to a lot of `mv`. Therefore, some relative paths were
wrong. In this commit the dependent files were also moved so that the paths
work again.

… expansion

…::root()`

For consistency with `ExpnId::root`.

Also introduce a helper `Span::with_root_ctxt` for creating spans with `SyntaxContext::root()` context

`Ident` has had a full span rather than just a `SyntaxContext` for a long time now.

The expansion info is not optional and should always exist

Traces already contain module info without that.
It's easy to forget to call `finalize_*` on a module.
In particular, macros enum and trait modules weren't finalized.
By happy accident macros weren't placed into those modules until now.

The previous approach was brittle - what would happen if `ParentScope` wasn't created by `invoc_parent_scope`?
That's exactly the case for various uses of `ParentScope` in diagnostics and in built-in attribute validation.

Remove some unnecessary parameters from functions

It was very similar to `ParentScope` and mostly could be replaced by it.

By allocating its derive paths on the resolver arena.

It was introduced to avoid going through `hygiene_data`, but now it's read only once, when `ParseSess` is created, so going through a lock is ok.

For naming consistency with everything else in this area

Group all ABI tests.

r? @eddyb

Closes rust-lang#62401

…hton

Use libunwind from llvm-project submodule for musl targets

This avoid downloading libunwind by using the scheme introduced in rust-lang#61544

Continue refactoring resolve and hygiene

The general goal is addressing FIXMEs from the previous PRs.

Merging similar data structures (+ prerequisites for such merging), accounting for the fact that all `ExpnId`s have associated data in `HygieneData` now (less `Option`s).

Also, some renaming.
This should be the last renaming session in this area, I think.

r? @matthewjasper

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

… r=alexreg

libcore: more cleanups using `#![feature(associated_type_bounds)]`

Turns out this was indeed a bootstrapping issue from a test with `./x.py check` locally after rust-lang#63534 merged.

Closes rust-lang#63393

r? @alexreg
cc @iluuu1994
cc rust-lang#52662

…tril

Do not suggest `try_into` for base types inside of macro expansions

Fix typo in DoubleEndedIterator::nth_back doc