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_mir_transform/src/errors.rs

@@ -89,7 +89,7 @@ pub(crate) struct FnItemRef {
     pub ident: String,
 }
 
-pub(crate) struct MustNotSupend<'tcx, 'a> {
+pub(crate) struct MustNotSupend<'a, 'tcx> {
     pub tcx: TyCtxt<'tcx>,
     pub yield_sp: Span,
     pub reason: Option<MustNotSuspendReason>,