Auto merge of #97313 - cjgillot:ast-lifetimes-anon, r=petrochenkov

Resolve function lifetime elision on the AST

~Based on #97720

Lifetime elision for functions is purely syntactic in nature, so can be resolved on the AST.
This PR replicates the elision logic and diagnostics on the AST, and replaces HIR-based resolution by a `delay_span_bug`.

This refactor allows for more consistent diagnostics, which don't have to guess the original code from HIR.

r? `@petrochenkov`

Author: bors

compiler/rustc_ast_lowering/src/lib.rs

@@ -1835,7 +1835,6 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         debug!(?self.captured_lifetimes);
         let name = match res {
             LifetimeRes::Param { mut param, binder } => {
-                debug_assert_ne!(ident.name, kw::UnderscoreLifetime);
                 let p_name = ParamName::Plain(ident);
                 if let Some(mut captured_lifetimes) = self.captured_lifetimes.take() {
                     if !captured_lifetimes.binders_to_ignore.contains(&binder) {

compiler/rustc_hir/src/def.rs

@@ -713,7 +713,7 @@ impl<Id> Res<Id> {
 }
 
 /// Resolution for a lifetime appearing in a type.
-#[derive(Copy, Clone, Debug)]
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
 pub enum LifetimeRes {
     /// Successfully linked the lifetime to a generic parameter.
     Param {