The data-shape check answered a type that refers back to a type still
being checked as a data shape and recorded that answer before the
outer check finished. With `Branch { child: Tree; handle: Handle }` and
`Tree { parent: Branch | null }`, checking Branch first recorded Tree as
a data shape, and Tree was re-exported although Branch reaches an
interface with a method. The check now walks every type reachable from
the queried one before it records any of them as a data shape, and
records the types on the path to a non-data type as non-data.
Chris Tate
47ba594c3f