This makes the transition easier as e.g. allow directives
won't fire the unknown lint warning once it is turned to
warn by default in the future. This is especially
important compared to other lints in the unused group
because the _ prefix trick doesn't exist for macro rules,
so allowing is the only option (either of unused_macro_rules,
or of the entire unused group, but that is not as informative
to readers). Allowing the lint also makes it possible to work
on possible heuristics for disabling the macro in specific
cases.

Make write/print macros eagerly drop temporaries

This PR fixes the 2 regressions in rust-lang#96434 (`println` and `eprintln`) and changes all the other similar macros (`write`, `writeln`, `print`, `eprint`) to match the old pre-rust-lang#94868 behavior of `println` and `eprintln`.

argument position | before rust-lang#94868 | after rust-lang#94868 | after this PR
--- |:---:|:---:|:---:
`write!($tmp, "…", …)` | :rage: | :rage: | :smiley_cat:
`write!(…, "…", $tmp)` | :rage: | :rage: | :smiley_cat:
`writeln!($tmp, "…", …)` | :rage: | :rage: | :smiley_cat:
`writeln!(…, "…", $tmp)` | :rage: | :rage: | :smiley_cat:
`print!("…", $tmp)` | :rage: | :rage: | :smiley_cat:
`println!("…", $tmp)` | :smiley_cat: | :rage: | :smiley_cat:
`eprint!("…", $tmp)` | :rage: | :rage: | :smiley_cat:
`eprintln!("…", $tmp)` | :smiley_cat: | :rage: | :smiley_cat:
`panic!("…", $tmp)` | :smiley_cat: | :smiley_cat: | :smiley_cat:

Example of code that is affected by this change:

```rust
use std::sync::Mutex;

fn main() {
    let mutex = Mutex::new(0);
    print!("{}", mutex.lock().unwrap()) /* no semicolon */
}
```

You can see several real-world examples like this in the Crater links at the top of rust-lang#96434. This code failed to compile prior to this PR as follows, but works after this PR.

```console
error[E0597]: `mutex` does not live long enough
 --> src/main.rs:5:18
  |
5 |     print!("{}", mutex.lock().unwrap()) /* no semicolon */
  |                  ^^^^^^^^^^^^---------
  |                  |
  |                  borrowed value does not live long enough
  |                  a temporary with access to the borrow is created here ...
6 | }
  | -
  | |
  | `mutex` dropped here while still borrowed
  | ... and the borrow might be used here, when that temporary is dropped and runs the `Drop` code for type `MutexGuard`
```

Use pointers in `cell::{Ref,RefMut}` to avoid `noalias`

When `Ref` and `RefMut` were based on references, they would get LLVM `noalias` attributes that were incorrect, because that alias guarantee is only true until the guard drops. A `&RefCell` on the same value can get a new borrow that aliases the previous guard, possibly leading to miscompilation. Using `NonNull` pointers in `Ref` and `RefCell` avoids `noalias`.

Fixes the library side of rust-lang#63787, but we still might want to explore language solutions there.

…enkov

Allow the unused_macro_rules lint for now

It was newly added by rust-lang#96150 with warn by default, which is great as it gave exposure to the community, and their feedback gave me ideas for improvements.

Allowing the lint is good for two reasons:

* It makes the transition easier as e.g. allow directives won't fire the unknown lint warning once it is turned to warn by default in the future. The [commit that allowed the lint in fuchsia](https://fuchsia.googlesource.com/fuchsia/+/9d8f96517c3963de2f0e25598fd36061914524cd%5E%21/) had to allow unknown lints for example.
This is especially important compared to other lints in the unused group,
because the _ prefix trick doesn't exist for macro rules, allowing is the
only option (either of unused_macro_rules, or of the entire unused group,
but that is not as informative to readers). Allowing the lint also makes it
possible to work on possible heuristics for disabling the macro in specific
cases.
* It gives time for implementing heuristics for when to suppress the lint, e.g.
when `compile_error!` is invoked by that arm (so it's only there to yield an error).

See: rust-lang#96150 (comment)

I would also like this to be backported to the 1.62 beta branch (cc rust-lang#97016).

…r=notriddle

Add new eslint rule about brace style

It also prevents one liners.

r? `@notriddle`