Fix #316 polymorphic create fragment

[dwickern]

I fixed the merge conflicts from #436 and got it working with the new RecordData implementation.

Fixes #316 Closes #436

[dwickern]

There seems to be a problem still with polymorphic values in fragmentArrays when using createRecord:

const zoo = store.createRecord('zoo', {
  star: { $type: 'lion' },
  animals: [{ $type: 'lion' }, { $type: 'elephant' }],
});
zoo.star instanceof Lion; // true ✅
zoo.animals.firstObject instanceof Lion; // false ❌
zoo.animals.lastObject instanceof Elephant; // false ❌

Edit: resolved by 15fac61a31126f94094e5872c4f71a78e451b488

[knownasilya]

@dwickern ready for review?

[dwickern]

@knownasilya ready for review 👍

[dwickern]

@knownasilya any plans to release this fix?

[knownasilya]

@dwickern released