`onSnapshot` is missing on DocumentReferences created through `DocumentSnapshot.data()`

[posva]

Describe your environment

• Operating System version: osx
• Browser version: edge 87
• Firebase SDK version: 8.1.1
• Firebase Product: firestore

Describe the problem

References read through a DocumentSnapshot.data() are not DocumentReference and are missing the onSnapshot function. This was present on v7 and it's useful for Vuefire to automatically listen to changes in nested references

Steps to reproduce:

• Create a document with a reference to another document
• Listen to changes through onSnapshot

Relevant Code:

(The stackblitz demo doesn't seem to work after upgrading firebase to 8.1.1). hopefull this code should give more context about seems like a regression

var db = firebase
  .initializeApp({
    projectId: "vue-fire-store",
    databaseURL: "https://vue-fire-store.firebaseio.com"
  })
  .firestore();

db.collection("tweets").onSnapshot(snaphot => {
  const changes = snapshot.docChanges();
  changes.added.forEach(({ doc }) => {
     doc.data().tweet.onSnaphot // undefined
  })
});

[dconeybe]

This looks like a duplicate of #4125. If so, you could using version 8.0.2 until a fix is ready. Let me know if this works for you.

[posva]

Oh sorry, I didn't find the duplicate! It is indeed the same