FindAllReferences on Length property or Slice method misses usages in list-patterns

[jcouv]

FAR doesn't understand properties/indexers/methods that are used in list-patterns yet.

_ = new Collection() is [1, 2];
class Collection
{
   public int Length => 0;
   public object this[int i] => null;
   public Collection Slice(int i, int j) => null;
}

Relates to test plan #51289

[CyrusNajmabadi]

Moving out of 17.1 we def don't need this immediately. Note: this would be a good way for someone to learn how to update FAR/indices.