syntax: Remove use of `pub use` globs

`quote_expr!` now injects two more (priv) `use` globs.
This may cause extra unused_imports warning.
rustdoc: Deduplicate lists of implementors

Inlining caused implementors to show up multiple times.

cc #14584
rustdoc: Correctly inline required/provided methods

Apparently relying on provided_source in ty::Method is unreliable!

Closes #14594
test: Add tests for closed issue #10764

Closes #10764
Improve code reuse in check_match::specialize()
Remove further code duplication
auto merge of #14509 : klutzy/rust/de-pub-use-glob, r=alexcrichton

This patchset removes `pub use` usage except for `test/`.
cc #11870
Document failure cases for `char_at` and friends.
auto merge of #14598 : alexcrichton/rust/triage, r=huonw

Closes #10764
auto merge of #14601 : skade/rust/remove-notrust-tags, r=alexcrichton

Now that rustdoc understands proper language tags
as the code not being Rust, we can tag everything
properly. `norust` as a negative statement is a bad
tag.

This change tags examples in other languages by
their language. Plain notations are marked as `text`.
Console examples are marked as `console`.

Also fix markdown.rs to not highlight non-rust code.

Amends the documentation to reflect the new
behaviour.
Adding show impl for Rc
auto merge of #14605 : jakub-/rust/pattern-matching-refactor, r=pcwalton

I've been working around these parts of code and it seems like it could use a bit of a refactor. This is the first step.
std: add `IterReader` to adapt iterators into readers
auto merge of #14609 : aturon/rust/issue-12882, r=alexcrichton
Update README file for src/ directory
Add next_permutation and prev_permutation onto MutableOrdVector<T>.

Unlike ImmutableClonableVector::permutations() which returns an iterator,
cloning the entire array each iteration, these methods mutate the vector in-place.
For that reason, these methods are much faster; between 35-55 times faster,
depending on the benchmark. They also generate permutations in lexicographical order.
Doc: grammar fix in intro.md
auto merge of #14621 : Sawyer47/rust/fix-readme, r=alexcrichton
Implement ToJson for &[T], and add tests. Closes #14619
syntax: Make quasiquoter use absolute paths

As part of removing `pub use` glob, two extra import globs were
injected to make `quote_expr!` work. However the globs caused
`unused_import` warning in some places.

Quasiquoter needed the globs since it generated idents (e.g. `TyU`)
rather than absolute paths (`::syntax::ast::TyU`).
This patch removes the extra globs and makes quasiquoter use absolute
paths.

Fixes #14618