Use `fn` ptr signature instead of `{closure@..}` in infer error

When suggesting a type on inference error, do not use `{closure@..}`.
Instead, replace with an appropriate `fn` ptr.

On the error message, use `short_ty_string` and write long types to
disk.

```
error[E0284]: type annotations needed for `Select<{closure@lib.rs:2782:13}, _, Expression<'_>, _>`
  --> crates/lang/src/parser.rs:41:13
   |
41 |         let lit = select! {
   |             ^^^
42 |             Token::Int(i) = e => Expression::new(Expr::Lit(ast::Lit::Int(i.parse().unwrap())), e.span()),
   |                                                                                                  ---- type must be known at this point
   |
   = note: the full type name has been written to '/home/gh-estebank/iowo/target/debug/deps/lang-e2d6e25819442273.long-type-4587393693885174369.txt'
   = note: cannot satisfy `<_ as chumsky::input::Input<'_>>::Span == SimpleSpan`
help: consider giving `lit` an explicit type, where the type for type parameter `I` is specified
   |
41 |         let lit: Select<for<'a, 'b> fn(tokens::Token<'_>, &'a mut MapExtra<'_, 'b, _, _>) -> Option<Expression<'_>>, _, Expression<'_>, _> = select! {
   |                +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
```

instead of

```
error[E0284]: type annotations needed for `Select<{closure@/home/gh-estebank/.cargo/registry/src/index.crates.io-6f17d22bba15001f/chumsky-1.0.0-alpha.6/src/lib.rs:2782:13: 2782:28}, _, Expression<'_>, _>`
  --> crates/lang/src/parser.rs:41:13
   |
41 |         let lit = select! {
   |             ^^^
42 |             Token::Int(i) = e => Expression::new(Expr::Lit(ast::Lit::Int(i.parse().unwrap())), e.span()),
   |                                                                                                  ---- type must be known at this point
   |
   = note: cannot satisfy `<_ as chumsky::input::Input<'_>>::Span == SimpleSpan`
help: consider giving `lit` an explicit type, where the type for type parameter `I` is specified
   |
41 |         let lit: Select<{closure@/home/gh-estebank/.cargo/registry/src/index.crates.io-6f17d22bba15001f/chumsky-1.0.0-alpha.6/src/lib.rs:2782:13: 2782:28}, _, Expression<'_>, _> = select! {
   |                ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
```

Fix #123630.

2 files changed, 2 insertions, 2 deletions

diff --git a/tests/ui/generic-const-items/inference-failure.stderr b/tests/ui/generic-const-items/inference-failure.stderr
index 10ecd83ec53..594743a47f4 100644
--- a/tests/ui/generic-const-items/inference-failure.stderr
+++ b/tests/ui/generic-const-items/inference-failure.stderr
@@ -1,4 +1,4 @@
-error[E0282]: type annotations needed for `Option<T>`
+error[E0282]: type annotations needed for `Option<_>`
   --> $DIR/inference-failure.rs:8:9
    |
 LL |     let _ = NONE;
diff --git a/tests/ui/generic-const-items/parameter-defaults.stderr b/tests/ui/generic-const-items/parameter-defaults.stderr
index b8220af5d0e..13562c98f6d 100644
--- a/tests/ui/generic-const-items/parameter-defaults.stderr
+++ b/tests/ui/generic-const-items/parameter-defaults.stderr
@@ -4,7 +4,7 @@ error: defaults for type parameters are only allowed in `struct`, `enum`, `type`
 LL | const NONE<T = ()>: Option<T> = None::<T>;
    |            ^^^^^^
 
-error[E0282]: type annotations needed for `Option<T>`
+error[E0282]: type annotations needed for `Option<_>`
   --> $DIR/parameter-defaults.rs:13:9
    |
 LL |     let _ = NONE;