Fix hard lifetime error

```
error[E0478]: lifetime bound not satisfied
   --> compiler/rustc_infer/src/infer/nll_relate/mod.rs:794:8
    |
794 |     D: TypeRelatingDelegate<'cx, 'tcx>,
    |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
note: lifetime parameter instantiated with the lifetime `'tcx` as defined on the struc
t at 792:29
   --> compiler/rustc_infer/src/infer/nll_relate/mod.rs:792:29
    |
792 | struct TypeGeneralizer<'cx, 'tcx, D>
    |                             ^^^^
note: but lifetime parameter must outlive the lifetime `'cx` as defined on the struct
at 792:24
   --> compiler/rustc_infer/src/infer/nll_relate/mod.rs:792:24
    |
792 | struct TypeGeneralizer<'cx, 'tcx, D>
    |                        ^^^
```

Author: jyn514

compiler/rustc_infer/src/infer/nll_relate/mod.rs

@@ -791,6 +791,7 @@ impl<'me, 'tcx> TypeVisitor<'tcx> for ScopeInstantiator<'me, 'tcx> {
 /// [blog post]: https://is.gd/0hKvIr
 struct TypeGeneralizer<'cx, 'tcx, D>
 where
+    'tcx: 'cx,
     D: TypeRelatingDelegate<'cx, 'tcx>,
 {
     _tcx: PhantomData<(&'cx (), &'tcx ())>,
@@ -813,9 +814,9 @@ where
     universe: ty::UniverseIndex,
 }
 
-impl<D> TypeRelation<'tcx> for TypeGeneralizer<'me, 'tcx, D>
+impl<D> TypeRelation<'tcx> for TypeGeneralizer<'cx, 'tcx, D>
 where
-    D: TypeRelatingDelegate<'me, 'tcx>,
+    D: TypeRelatingDelegate<'cx, 'tcx>,
 {
     fn tcx(&self) -> TyCtxt<'tcx> {
         self.delegate.infcx().tcx