Previously we weren't properly checking that using
`-fexperimental-late-parse-attributes` worked on source code that didn't
need late parsing.
For example we weren't testing that the attribute appearing in the type
position generated the right AST with
`-fexperimental-late-parse-attributes` off.
This patch adds additional `RUN` lines to re-run the relevant test cases
with `-fexperimental-late-parse-attributes` enabled.
rdar://133325597
The attributes `sized_by`, `counted_by_or_null` and `sized_by_or_null`
have been added as variants on `counted_by`, each with slightly
different semantics. `sized_by` takes a byte size parameter instead of
an element count, allowing pointees with unknown size. The
`counted_by_or_null` and `sized_by_or_null` variants are equivalent to
their base variants, except the pointer can be null regardless of
count/size value. If the pointer is null the size is effectively 0.
rdar://125400354
