It has implementation consequences to refer to classes that are not
declared in dart:core, and it increases the library/spec interaction surface.
This change removes all references to `LinkedHashSet` from the spec.
It changess the rule for when a `{}` is a set to be
context type is a subtype of `FutureOr^\inf(Iterable<Object>)`
and not a subtupe of `FutureOr^\inf(Map<Object,Object>)`.
That should *work* for
* `Iterable<X>`
* `Set<X>`
* `LinkedHashSet<X>`
* `HashSet<X>`
* `FutureOr<Set<X>>`
(with likely exect-type issues as usual).
Change-Id: I3074da27b36093075c8c83e9672bf2fdec135c1c
Reviewed-on: https://dart-review.googlesource.com/c/87972
Commit-Queue: Lasse R.H. Nielsen <lrn@google.com>
Reviewed-by: Erik Ernst <eernst@google.com>
Lasse R.H. Nielsen
c565d4e477