Rename and reorder lots of lifetimes.

- Replace non-standard names like 's, 'p, 'rg, 'ck, 'parent, 'this, and
  'me with vanilla 'a. These are cases where the original name isn't
  really any more informative than 'a.
- Replace names like 'cx, 'mir, and 'body with vanilla 'a when the lifetime
  applies to multiple fields and so the original lifetime name isn't
  really accurate.
- Put 'tcx last in lifetime lists, and 'a before 'b.

compiler/rustc_ty_utils/src/layout_sanity_check.rs

@@ -28,7 +28,7 @@ pub(super) fn sanity_check_layout<'tcx>(
     }
 
     /// Yields non-ZST fields of the type
-    fn non_zst_fields<'tcx, 'a>(
+    fn non_zst_fields<'a, 'tcx>(
         cx: &'a LayoutCx<'tcx, TyCtxt<'tcx>>,
         layout: &'a TyAndLayout<'tcx>,
     ) -> impl Iterator<Item = (Size, TyAndLayout<'tcx>)> + 'a {