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_const_eval/src/check_consts/check.rs

@@ -166,12 +166,12 @@ impl<'mir, 'tcx> Qualifs<'mir, 'tcx> {
     }
 }
 
-struct LocalReturnTyVisitor<'ck, 'mir, 'tcx> {
+struct LocalReturnTyVisitor<'a, 'mir, 'tcx> {
     kind: LocalKind,
-    checker: &'ck mut Checker<'mir, 'tcx>,
+    checker: &'a mut Checker<'mir, 'tcx>,
 }
 
-impl<'ck, 'mir, 'tcx> TypeVisitor<TyCtxt<'tcx>> for LocalReturnTyVisitor<'ck, 'mir, 'tcx> {
+impl<'a, 'mir, 'tcx> TypeVisitor<TyCtxt<'tcx>> for LocalReturnTyVisitor<'a, 'mir, 'tcx> {
     fn visit_ty(&mut self, t: Ty<'tcx>) {
         match t.kind() {
             ty::FnPtr(..) => {}