Support multi-character punct tokens in MBE
Fixes#11497
In the context of MBE, consecutive puncts are parsed as multi-character punct tokens whenever possible. For example, `:::` is parsed as ``[Punct(`::`), Punct(`:`)]`` and shouldn't get matched to patterns like `: : :` or `: ::`.
We have implemented this behavior only for when we match puncts against `tt` fragments, but not when we match puncts literally. This PR extracts the multi-character punct handling procedure into a separate method and extends its support for literal matching.
For good measure, this PR adds support for `<-` token, which is still [considered as one token in rustc](e396186407/compiler/rustc_ast/src/token.rs (L249)) despite the placement syntax having been removed.
Use `rustc_safe_intrinsic` attribute to check for intrinsic safety
Instead of maintaining a list that is poorly kept in sync we can just use the attribute.
This will make new RA versions unusable with old toolchains that don't have the attribute yet. Should we keep maintaining the list as a fallback or just don't care?
This makes code more readale and concise,
moving all format arguments like `format!("{}", foo)`
into the more compact `format!("{foo}")` form.
The change was automatically created with, so there are far less change
of an accidental typo.
```
cargo clippy --fix -- -A clippy::all -W clippy::uninlined_format_args
```
Seems like these can be safely fixed. With one, I was particularly
surprised -- `Some(pats) => &**pats,` in body.rs?
```
cargo clippy --fix -- -A clippy::all -D clippy::explicit_auto_deref
```
I am not certain if this will improve performance,
but it seems having a .clone() without any need should be removed.
This was done with clippy, and manually reviewed:
```
cargo clippy --fix -- -A clippy::all -D clippy::redundant_clone
```
