Rollup merge of #99911 - cjgillot:no-guess, r=davidtwco

Remove some uses of `guess_head_span`

That function cuts a span at the first occurrence of `{`.  Using `def_span` is almost always more precise.

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -1946,7 +1946,6 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             ));
 
             let original_span = err.span.primary_span().unwrap();
-            let original_span = self.tcx.sess.source_map().guess_head_span(original_span);
             let mut span = MultiSpan::from_span(original_span);
 
             let message = outer_generator