Only look for complete suffixes or prefixes of irrefutable let patterns, so
that an irrefutable let pattern in a chain surrounded by refutable ones is
not linted, as it is an useful pattern.

Format core and std macro rules, removing needless surrounding blocks

Many of the asserting and printing macros in `core` and `std` are written with prehistoric-looking formatting, like this:

https://github.com/rust-lang/rust/blob/335ffbfa547df94ac236f5c56130cecf99c8d82b/library/std/src/macros.rs#L96-L101

In modern Rust style this would conventionally be written as follows instead, always using braces and a trailing semicolon on the macro arms:

https://github.com/rust-lang/rust/blob/af53809c874e0afb7be966df4d3cfcaa05277c53/library/std/src/macros.rs#L98-L105

Getting rid of the unneeded braces inside the expansion reduces extraneous indentation in macro-expanded code. For example:

```rust
println!("repro {}", true);
```

```rust
// before:

{
    ::std::io::_print(
        ::core::fmt::Arguments::new_v1(
            &["repro ", "\n"],
            &[::core::fmt::ArgumentV1::new_display(&true)],
        ),
    );
};
```

```rust
// after:

::std::io::_print(
    ::core::fmt::Arguments::new_v1(
        &["repro ", "\n"],
        &[::core::fmt::ArgumentV1::new_display(&true)],
    ),
);
```

…s, r=estebank

Extend the irrefutable_let_patterns lint to let chains

Implements the suggestion from rust-lang#94927 (comment)

We only look for complete suffixes or prefixes of irrefutable let patterns, so
that an irrefutable let pattern in a chain surrounded by refutable ones is
not linted, as it is an useful pattern that has no low-cost replacement (unlike suffixes or prefixes which can just be copied outside of the `if`: either into the `if`'s block, or the block surrounding the `if`).
If all patterns in a let chain are irrefutable, we lint as well.

Depends on rust-lang#94958 ~~so I included it into the PR for now~~ *which has been merged since*.

r? `@estebank`

cc `@joshtriplett` `@c410-f3r`

…rustc-parse, r=Dylan-DPC

Refactor: Use `format_args_capture` in some parts of `rustc_parse`

… r=Dylan-DPC

Improve the explanation about the behaviour of read_line

Close issue like rust-lang/book#2574

…et-else, r=joshtriplett

Ensure that `let_else` does not interact with `let_chains`

As requested on rust-lang#94927.

cc `@joshtriplett` `@estebank`