Rollup merge of rust-lang#127058 - compiler-errors:tighten-async-spans, r=oli-obk

Tighten `fn_decl_span` for async blocks

Tightens the span of `async {}` blocks in diagnostics, and subsequently async closures and async fns, by actually setting the `fn_decl_span` correctly. This is kinda a follow-up on rust-lang#125078, but it fixes the problem in a more general way.

I think the diagnostics are significantly improved, since we no longer have a bunch of overlapping spans. I'll point out one caveat where I think the diagnostic may get a bit more confusing, but where I don't think it matters.

r? ````@estebank```` or ````@oli-obk```` or someone else on wg-diag or compiler i dont really care lol

Author: matthiaskrgr

clippy_lints/src/suspicious_operation_groupings.rs

@@ -549,7 +549,7 @@ fn ident_difference_expr_with_base_location(
         | (Assign(_, _, _), Assign(_, _, _))
         | (TryBlock(_), TryBlock(_))
         | (Await(_, _), Await(_, _))
-        | (Gen(_, _, _), Gen(_, _, _))
+        | (Gen(_, _, _, _), Gen(_, _, _, _))
         | (Block(_, _), Block(_, _))
         | (Closure(_), Closure(_))
         | (Match(_, _, _), Match(_, _, _))

clippy_utils/src/ast_utils.rs

@@ -226,7 +226,7 @@ pub fn eq_expr(l: &Expr, r: &Expr) -> bool {
                 && eq_fn_decl(lf, rf)
                 && eq_expr(le, re)
         },
-        (Gen(lc, lb, lk), Gen(rc, rb, rk)) => lc == rc && eq_block(lb, rb) && lk == rk,
+        (Gen(lc, lb, lk, _), Gen(rc, rb, rk, _)) => lc == rc && eq_block(lb, rb) && lk == rk,
         (Range(lf, lt, ll), Range(rf, rt, rl)) => ll == rl && eq_expr_opt(lf, rf) && eq_expr_opt(lt, rt),
         (AddrOf(lbk, lm, le), AddrOf(rbk, rm, re)) => lbk == rbk && lm == rm && eq_expr(le, re),
         (Path(lq, lp), Path(rq, rp)) => both(lq, rq, eq_qself) && eq_path(lp, rp),