[Bug] Field type reference in DocumentSnapshot obtained in transaction is not an instance of DocumentReference

[rulamon]

[REQUIRED] Describe your environment

• Operating System version: Windows 10 Home 1909
• Browser version: Chrome 87
• Firebase SDK version: 8.1.2
• Firebase Product: firestore

[REQUIRED] Describe the problem

When getting a document through a transaction (Transaction.get()) the field type reference does not does not return an instance of DocumentReference anymore. Similar to #4125 but with transactions instead of queries.

[schmidt-sebastian]

Thanks for reporting this. We will get this fixed in the next release, which unfortunately is not slated to happen until the beginning of January.