fix(afs): fix collection add return type

[Tiedye]

Checklist

• Issue number for this PR: AngularFirestoreCollection add method doesn't all return AngularFirestoreDocument type #2000
• Docs included?: yes
• Test units included?: no
• In a clean directory, yarn install, yarn test run successfully? yes

Description

The method AngularFirestoreCollection.add is not consistent with AngularFirestoreCollection.doc and returns a class of type Promise<firebase.firestore.DocumentReference> instead of a Promise<AngularFirestoreDocument<T>>.

This is a breaking change of a previously undocumented behaviour.

Code sample

This

const newDoc = this.afStore.doc<A>(await this.afStore.collection<A>('drafts').add({...}));

becomes

const newDoc = await this.afStore.collection<A>('drafts').add({...});

[googlebot]

Thanks for your pull request. It looks like this may be your first contribution to a Google open source project (if not, look below for help). Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

📝 Please visit https://cla.developers.google.com/ to sign.

Once you've signed (or fixed any issues), please reply here (e.g. I signed it!) and we'll verify it.

---

What to do if you already signed the CLA

Individual signers

• It's possible we don't have your GitHub username or you're using a different email address on your commit. Check your existing CLA data and verify that your email is set on your git commits.

Corporate signers

• Your company has a Point of Contact who decides which employees are authorized to participate. Ask your POC to be added to the group of authorized contributors. If you don't know who your Point of Contact is, direct the Google project maintainer to go/cla#troubleshoot (Public version).
• The email used to register you as an authorized contributor must be the email used for the Git commit. Check your existing CLA data and verify that your email is set on your git commits.
• The email used to register you as an authorized contributor must also be attached to your GitHub account.

[googlebot]

Thanks for your pull request. It looks like this may be your first contribution to a Google open source project (if not, look below for help). Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

📝 Please visit https://cla.developers.google.com/ to sign.

Once you've signed (or fixed any issues), please reply here (e.g. I signed it!) and we'll verify it.

---

What to do if you already signed the CLA

Individual signers

• It's possible we don't have your GitHub username or you're using a different email address on your commit. Check your existing CLA data and verify that your email is set on your git commits.

Corporate signers

• Your company has a Point of Contact who decides which employees are authorized to participate. Ask your POC to be added to the group of authorized contributors. If you don't know who your Point of Contact is, direct the Google project maintainer to go/cla#troubleshoot (Public version).
• The email used to register you as an authorized contributor must be the email used for the Git commit. Check your existing CLA data and verify that your email is set on your git commits.
• The email used to register you as an authorized contributor must also be attached to your GitHub account.

[Tiedye]

I signed it!

[googlebot]

CLAs look good, thanks!

[googlebot]

CLAs look good, thanks!

[jamesdaniels]

FYI I've asked David to review as this is an API change. As such we wouldn't be able to merge to v6 if we want to go this direction.

[jamesdaniels]

Thanks for this contribution, we opted to go a different direction in v7 however and no longer have a AngularFirestoreDocument (outside of compat which I consider for the most-part feature complete).