Rollup merge of rust-lang#89895 - camsteffen:for-loop-head-span, r=davidtwco

Don't mark for loop iter expression as desugared

We typically don't mark spans of lowered things as desugared. This helps Clippy rightly discern when code is (not) from expansion. This was discovered by ``@flip1995`` at rust-lang/rust-clippy#7789 (comment).

Author: JohnTitor

clippy_lints/src/vec.rs

@@ -63,13 +63,7 @@ impl<'tcx> LateLintPass<'tcx> for UselessVec {
             if is_copy(cx, vec_type(cx.typeck_results().expr_ty_adjusted(arg)));
             then {
                 // report the error around the `vec!` not inside `<std macros>:`
-                let span = arg.span
-                    .ctxt()
-                    .outer_expn_data()
-                    .call_site
-                    .ctxt()
-                    .outer_expn_data()
-                    .call_site;
+                let span = arg.span.ctxt().outer_expn_data().call_site;
                 self.check_vec_macro(cx, &vec_args, Mutability::Not, span);
             }
         }