Previously, the `Number` part of the EBNF grammar had an option for `'.' Digit*`, which would include the string "." (a single decimal point). This is not valid, and does not return an Ok as stated. The corrected version removes this, and still allows for the `'.' Digit+` case with the already existing `Digit* '.' Digit+` case.

Expose `get_many_mut` and `get_many_unchecked_mut` to HashMap

This pull-request expose the function [`get_many_mut`](https://docs.rs/hashbrown/0.12.0/hashbrown/struct.HashMap.html#method.get_many_mut) and [`get_many_unchecked_mut`](https://docs.rs/hashbrown/0.12.0/hashbrown/struct.HashMap.html#method.get_many_unchecked_mut) from `hashbrown` to the standard library `HashMap` type. They obviously keep the same API and are added under the (new) `map_many_mut` feature.

- `get_many_mut`: Attempts to get mutable references to `N` values in the map at once.
- `get_many_unchecked_mut`: Attempts to get mutable references to `N` values in the map at once, without validating that the values are unique.

Diagnose anonymous lifetimes errors more uniformly between async and regular fns

Async fns and regular fns are desugared differently.  For the former, we create a generic parameter at HIR level.  For the latter, we just create an anonymous region for typeck.

I plan to migrate regular fns to the async fn desugaring.

Before that, this PR attempts to merge the diagnostics for both cases.

r? `@estebank`

simplify code of finding arg index in `opt_const_param_of`

From the FIXME in the impl of `opt_const_param_of`. Part of the code is simplified by blending two iterator statements and using `let...else` statement.

…=Mark-Simulacrum

Be a little nicer with casts when formatting `fn` pointers

This removes a `fn(...) -> ...` -> `usize` -> `*const ()` -> `usize` cast. cc rust-lang#95489.

Corrected EBNF grammar for from_str

Hello! This is my first time contributing to an open-source project. I'm excited to have the chance to contribute to the rust community 🥳

I noticed an issue with the documentation for `from_str` in `f32` and `f64`. It states that "All strings that adhere to the following [EBNF](https://www.w3.org/TR/REC-xml/#sec-notation) grammar when lowercased will result in an `Ok` being returned. I believe this is incorrect for the string `"."`, which is valid for the given EBNF grammar, but does not result in an `Ok` being returned ([playground](https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=09f891aa87963a56d3b0d715d8cbc2b4)). I have simplified the grammar in a way which fixes that, but is otherwise identical.

Previously, the `Number` part of the EBNF grammar had an option for `'.' Digit*`, which would include the string `"."`. This is not valid, and does not return an Ok as stated. The corrected version removes this, and still allows for the `'.' Digit+` case with the already existing `Digit* '.' Digit+` case.