Rollup merge of #104199 - SarthakSingh31:issue-97417-1, r=cjgillot

Keep track of the start of the argument block of a closure

This removes a call to `tcx.sess.source_map()` from [compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs](https://github.com/rust-lang/rust/compare/master...SarthakSingh31:issue-97417-1?expand=1#diff-8406bbc0d0b43d84c91b1933305df896ecdba0d1f9269e6744f13d87a2ab268a) as required by #97417.

VsCode automatically applied `rustfmt` to the files I edited under `src/tools`. I can undo that if its a problem.

r? `@cjgillot`

compiler/rustc_expand/src/build.rs

@@ -539,6 +539,9 @@ impl<'a> ExtCtxt<'a> {
                 fn_decl,
                 body,
                 fn_decl_span: span,
+                // FIXME(SarthakSingh31): This points to the start of the declaration block and
+                // not the span of the argument block.
+                fn_arg_span: span,
             })),
         )
     }