…nethercote

improve diagnostics for empty attributes

Adds a note about them not having any effect. This was previously done for `feature` attributes but no other attributes. In [converting the `feature` parser](rust-lang#146652) I removed that note. This PR adds it back in and makes it so all attributes benefit from it.

Not blocked on rust-lang#146652, either can merge first

impl Ord for params and use unstable sort

AFAICT we are only sorting to find duplicates, so unstable sort should work fine, and maybe is a tiny bit faster?

…jdonszelmann

Use `Iterator::eq` and (dogfood) `eq_by` in compiler and library

Now that rust-lang#137122 has landed, we can replace stuff that looks like:
```rust
let a: &[T];
let b: &[T];
let eq = a.len() == b.len() && a.iter().zip(b).all(|(a,b)| a == b)
```
with the much simpler `a.iter().eq(b)`, without losing the perf benefit of the different-length-fast-path.
Also dogfooded `Iterator::eq_by` (cc rust-lang#64295 ) while I'm at it.

First commit (4d1b6fa) should be very straightforward to review, second one (049a460) is slightly more creative, but IMHO a nice cleanup.

…mease

Fix removed version numbers of `doc_auto_cfg` and `doc_cfg_hide`

Tracking issue: rust-lang#43781

The `doc_auto_cfg` and `doc_cfg_hide` features were removed in a recent nightly (by rust-lang#138907).
I believe that the rustc version numbers at which the features were declared to be removed were incorrect, however, and should both be "1.92" (±1). As evidence in favour of this, the error we get from using this was:

```text
error[E0557]: feature has been removed
  --> src/lib.rs:22:29
   |
22 | #![cfg_attr(docsrs, feature(doc_auto_cfg))]
   |                             ^^^^^^^^^^^^ feature has been removed
   |
   = note: removed in 1.58.0; see <rust-lang#138907> for more information
   = note: merged into `doc_cfg`
```

Note especially the "removed in 1.58" claim. Further evidence is found in the comment further up this file: https://github.com/rust-lang/rust/blob/4ffeda10e10d4fa0c8edbd0dd9642d8ae7d3e66e/compiler/rustc_feature/src/removed.rs#L49-L53

I've chosen 1.92 as that was the milestone which rust-lang#138907 was added to.

cc `@GuillaumeGomez`

add joboet to library review rotation

Reviewing feels like fun again...