Add an optional Span to BrAnon and use it to print better error for HRTB error from generator interior

compiler/rustc_middle/src/ty/structural_impls.rs

@@ -68,7 +68,7 @@ impl<'tcx> fmt::Debug for ty::adjustment::Adjustment<'tcx> {
 impl fmt::Debug for ty::BoundRegionKind {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match *self {
-            ty::BrAnon(n) => write!(f, "BrAnon({:?})", n),
+            ty::BrAnon(n, span) => write!(f, "BrAnon({n:?}, {span:?})"),
             ty::BrNamed(did, name) => {
                 if did.is_crate_root() {
                     write!(f, "BrNamed({})", name)