DocumentReference and DocumentSnapshot typings are missing a generic

[AnthonyLenglet]

We've just ran into an issue that we hadn't noticed yet, the firestore.DocumentReference interface is missing a generic that is present in the firebase library

This missing caused a problem in this case, where discriminator was not required by in DocumentReference:

I also noticed the same issue with DocumentSnapshot

await firestore().collection('hello').doc(id).get()

returns Promise<firebase.firestore.DocumentSnapshot>

when in firebase it returns Promise<DocumentSnapshot<T>> with T = DocumentData

/**
  * Reads the document referred to by this `DocumentReference`.
  *
  * Note: By default, get() attempts to provide up-to-date data when possible
  * by waiting for data from the server, but it may return cached data or fail
  * if you are offline and the server cannot be reached. This behavior can be
  * altered via the `GetOptions` parameter.
  *
  * @param options An object to configure the get behavior.
  * @return A Promise resolved with a DocumentSnapshot containing the
  * current document contents.
  */
get(options?: GetOptions): Promise<DocumentSnapshot<T>>;

[BallisticPain]

I've noticed the CollectionReference is also missing the generics that are available in the SDK. I'm not sure if this was intentional or this library hasn't been updated to include them.