Try to suggest dereferences on trait selection failed

[ldm0]

Fixes #39029 Fixes #62530
This PR consists of two parts:

1. Decouple Autoderef with FnCtxt and move Autoderef to librustc_trait_selection.
2. Try to suggest dereferences when trait selection failed.

The first is needed because:

1. For suggesting dereferences, the struct Autoderef should be used. But before this PR, it is placed in librustc_typeck, which depends on librustc_trait_selection. But trait selection error emitting happens in librustc_trait_selection, if we want to use Autoderef in it, dependency loop is inevitable. So I moved the Autoderef to librustc_trait_selection.
2. Before this PR, FnCtxt is coupled to Autoderef, and FnCtxt only exists in librustc_typeck. So decoupling is needed.

After this PR, we can get suggestion like this:

error[E0277]: the trait bound `&Baz: Happy` is not satisfied
  --> $DIR/trait-suggest-deferences-multiple.rs:34:9
   |
LL | fn foo<T>(_: T) where T: Happy {}
   |                          ----- required by this bound in `foo`
...
LL |     foo(&baz);
   |         ^^^^
   |         |
   |         the trait `Happy` is not implemented for `&Baz`
   |         help: consider adding dereference here: `&***baz`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0277`.

r? @estebank

[bors]

☔ The latest upstream changes (presumably #72256) made this pull request unmergeable. Please resolve the merge conflicts.

[bors]

☔ The latest upstream changes (presumably #72778) made this pull request unmergeable. Please resolve the merge conflicts.

[rust-highfive]

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extracting /checkout/obj/build/cache/2020-04-22/rustfmt-nightly-x86_64-unknown-linux-gnu.tar.xz
error: failed to resolve patches for `https://github.com/rust-lang/crates.io-index`

Caused by:
  patch for `rustfmt-nightly` in `https://github.com/rust-lang/crates.io-index` did not resolve to any crates. If this is unexpected, you may wish to consult: https://github.com/rust-lang/cargo/issues/4678
Build completed unsuccessfully in 0:00:20
== clock drift check ==
  local time: Sat May 30 19:02:45 UTC 2020
  network time: Sat, 30 May 2020 19:02:45 GMT
  network time: Sat, 30 May 2020 19:02:45 GMT
== end clock drift check ==

##[error]Bash exited with code '1'.
##[section]Finishing: Run build
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[bors]

☔ The latest upstream changes (presumably #73504) made this pull request unmergeable. Please resolve the merge conflicts.

[estebank]

Apologies for the delay on reviewing this. I have a couple of nitpicks. Could you address them as you rebase? Other than that, I'm happy with the changes!

[ldm0]

Rebase done, nitpicks applied.

[estebank]

@bors r+

[bors]

📌 Commit f1e0710 has been approved by estebank