Auto merge of #132147 - estebank:long-types-2, r=davidtwco

Tweak E0277 output when a candidate is available

*Follow up to #132086.*

Go from

```
error[E0277]: the trait bound `Then<Ignored<chumsky::combinator::Filter<chumsky::primitive::Any<&str, chumsky::extra::Full<EmptyErr, (), ()>>, {closure@src/main.rs:9:17: 9:27}>, char>, chumsky::combinator::Map<impl CSTParser<'a, O>, O, {closure@src/main.rs:11:24: 11:27}>, (), (), chumsky::extra::Full<EmptyErr, (), ()>>: CSTParser<'a>` is not satisfied
 --> src/main.rs:7:50
  |
7 | fn leaf<'a, O>(parser: impl CSTParser<'a, O>) -> impl CSTParser<'a, ()> {
  |                                                  ^^^^^^^^^^^^^^^^^^^^^^ the trait `chumsky::private::ParserSealed<'_, &str, (), chumsky::extra::Full<EmptyErr, (), ()>>` is not implemented for `Then<Ignored<Filter<Any<&str, ...>, ...>, ...>, ..., ..., ..., ...>`, which is required by `Then<Ignored<chumsky::combinator::Filter<chumsky::primitive::Any<&str, chumsky::extra::Full<EmptyErr, (), ()>>, {closure@src/main.rs:9:17: 9:27}>, char>, chumsky::combinator::Map<impl CSTParser<'a, O>, O, {closure@src/main.rs:11:24: 11:27}>, (), (), chumsky::extra::Full<EmptyErr, (), ()>>: CSTParser<'a>`
  |
  = help: the trait `chumsky::private::ParserSealed<'_, &'a str, ((), ()), chumsky::extra::Full<EmptyErr, (), ()>>` is implemented for `Then<Ignored<chumsky::combinator::Filter<chumsky::primitive::Any<&str, chumsky::extra::Full<EmptyErr, (), ()>>, {closure@src/main.rs:9:17: 9:27}>, char>, chumsky::combinator::Map<impl CSTParser<'a, O>, O, {closure@src/main.rs:11:24: 11:27}>, (), (), chumsky::extra::Full<EmptyErr, (), ()>>`
  = help: for that trait implementation, expected `((), ())`, found `()`
  = note: required for `Then<Ignored<Filter<Any<&str, ...>, ...>, ...>, ..., ..., ..., ...>` to implement `Parser<'_, &str, ()>`
note: required for `Then<Ignored<Filter<Any<&str, ...>, ...>, ...>, ..., ..., ..., ...>` to implement `CSTParser<'a>`
 --> src/main.rs:5:16
  |
5 | impl<'a, O, T> CSTParser<'a, O> for T where T: Parser<'a, &'a str, O> {}
  |                ^^^^^^^^^^^^^^^^     ^          ---------------------- unsatisfied trait bound introduced here
  = note: the full name for the type has been written to '/home/gh-estebank/longlong/target/debug/deps/longlong-0008f9a4f2023b08.long-type-13239977239800463552.txt'
  = note: consider using `--verbose` to print the full type name to the console
  = note: the full name for the type has been written to '/home/gh-estebank/longlong/target/debug/deps/longlong-0008f9a4f2023b08.long-type-13239977239800463552.txt'
  = note: consider using `--verbose` to print the full type name to the console
```

to

```
error[E0277]: the trait bound `Then<Ignored<chumsky::combinator::Filter<chumsky::primitive::Any<&str, chumsky::extra::Full<EmptyErr, (), ()>>, {closure@src/main.rs:9:17: 9:27}>, char>, chumsky::combinator::Map<impl CSTParser<'a, O>, O, {closure@src/main.rs:11:24: 11:27}>, (), (), chumsky::extra::Full<EmptyErr, (), ()>>: CSTParser<'a>` is not satisfied
  --> src/main.rs:7:50
   |
7  | fn leaf<'a, O>(parser: impl CSTParser<'a, O>) -> impl CSTParser<'a, ()> {
   |                                                  ^^^^^^^^^^^^^^^^^^^^^^ unsatisfied trait bound
...
11 |     ws.then(parser.map(|_| ()))
   |     --------------------------- return type was inferred to be `Then<Ignored<..., ...>, ..., ..., ..., ...>` here
   |
   = help: the trait `ParserSealed<'_, &_, (), Full<_, _, _>>` is not implemented for `Then<Ignored<..., ...>, ..., ..., ..., ...>`
           but trait `ParserSealed<'_, &'a _, ((), ()), Full<_, _, _>>` is implemented for it
   = help: for that trait implementation, expected `((), ())`, found `()`
   = note: required for `Then<Ignored<..., ...>, ..., ..., ..., ...>` to implement `Parser<'_, &str, ()>`
note: required for `Then<Ignored<..., ...>, ..., ..., ..., ...>` to implement `CSTParser<'a>`
  --> src/main.rs:5:16
   |
5  | impl<'a, O, T> CSTParser<'a, O> for T where T: Parser<'a, &'a str, O> {}
   |                ^^^^^^^^^^^^^^^^     ^          ---------------------- unsatisfied trait bound introduced here
   = note: the full name for the type has been written to '/home/gh-estebank/longlong/target/debug/deps/longlong-df9d52be87eada65.long-type-1337037744507305372.txt'
   = note: consider using `--verbose` to print the full type name to the console
```

* Remove redundant wording
* Introduce trait diff highlighting logic and use it
* Fix incorrect "long type written to path" logic (can be split off)
* Point at tail expression in more cases in E0277
* Avoid long primary span labels in E0277 by moving them to a `help`

Fix #132013.

There are individual commits that can be their own PR. If the review load is too big, happy to split them off.

Author: bors