… a pattern

Added tests and stderr output

Decouple `rustc_hir::print` into `rustc_hir_pretty`

High level summary:
- The HIR pretty printer, `rustc_hir::print` is moved into a new crate `rustc_hir_pretty`.
- `rustc_ast_pretty` and `rustc_errors` are dropped as `rustc_hir` dependencies.
- The dependence on HIR pretty is generally reduced, leaving `rustc_save_analysis`, `rustdoc`, `rustc_metadata`, and `rustc_driver` as the remaining clients.

The main goal here is to reduce `rustc_hir`'s dependencies and its size such that it can start and finish earlier, thereby working towards rust-lang#65031.

r? @Zoxc

Miri nits: comment and var name improvement

r? @eddyb

parser: recover on `...` as a pattern, suggesting `..`

Fixes rust-lang#70388

My first PR to rust. So please let me know if I'm doing something wrong.

simplify match stmt

We actually have a surprising amount of
```rust
match expr {
    $($p:pat)|+ => true,
    _ => false,
}
```
While I would prefer this to be replaced with `matches!`, most cases are
fairly readable anyway so we can just let them be for now.