By moving `block_on` to an auxiliary crate, we avoid having to keep a separate
copy of it in every async test.

(This also incorporates some small tweaks to the headers in `await_ready.rs`.)

This does change the external interface, but not in a way that will
cause any breakage because external users don't mention the lifetimes.

Giving them more typical names.

- Replace non-standard names like 's, 'p, 'rg, 'ck, 'parent, 'this, and
  'me with vanilla 'a. These are cases where the original name isn't
  really any more informative than 'a.
- Replace names like 'cx, 'mir, and 'body with vanilla 'a when the lifetime
  applies to multiple fields and so the original lifetime name isn't
  really accurate.
- Put 'tcx last in lifetime lists, and 'a before 'b.

Failing to do this results in the lint example output complaining
about the lint not existing instead of the thing the lint is supposed
to be complaining about.

coverage: Extract `executor::block_on` from several async coverage tests

By moving `block_on` to an auxiliary crate, we avoid having to keep a separate copy of it in every async test.

…r=compiler-errors

simd_shuffle: require index argument to be a vector

Remove some codegen hacks by forcing the SIMD shuffle `index` argument to be a vector, which means (thanks to rust-lang#128537) that it will automatically be passed as an immediate in LLVM. The only special-casing we still have is for the extra sanity-checks we add that ensure that the indices are all in-bounds. (And the GCC backend needs to do a bunch of work since the Rust intrinsic is modeled after what LLVM expects, which seems to be quite different from what GCC expects.)

Fixes rust-lang#128738, see that issue for more context.

…ChrisDenton

Stabilize entry_insert

This stabilises `HashMap::Entry::insert_entry`, following the FCP in tracking issue rust-lang#65225.

This was implemented in rust-lang#64656 five years ago.

Lifetime cleanups

The last commit is very opinionated, let's see how we go.

r? `@oli-obk`

…k-lint-doc, r=compiler-errors

docs: Enable required feature for 'closure_returning_async_block' lint

Failing to do this results in the lint example output complaining about the lint not existing instead of the thing the lint is supposed to be complaining about.

See <https://doc.rust-lang.org/rustc/lints/listing/allowed-by-default.html#closure-returning-async-block>:
![image](https://github.com/user-attachments/assets/78bae16f-3fb6-4d6d-b8aa-768b477cd187)

Fix `Parser::break_up_float`'s right span

```rs
use std::mem::offset_of;

fn main() {
    offset_of!((u8,), 0.0);
}
```
Before:
```
error[E0609]: no field `0` on type `u8`
    --> ./main.rs:4:25
     |
4    |       offset_of!((u8,), 0.0);
     |  _____--------------------^-
     | |     |
     | |     in this macro invocation
5    | | }
...    |
     |
     = note: this error originates in the macro `offset_of` (in Nightly builds, run with -Z macro-backtrace for more info)

error: aborting due to 1 previous error
```
After:
```
error[E0609]: no field `0` on type `u8`
 --> ./main.rs:4:25
  |
4 |     offset_of!((u8,), 0.0);
  |                         ^

error: aborting due to 1 previous error
```

---
`@rustbot` label +A-parser +D-imprecise-spans