Add firestore 2nd gen triggers

[colerogers]

Add support for 2nd gen firestore triggers!

import {
  onDocumentWritten,
  onDocumentCreated,
  onDocumentUpdated,
  onDocumentDeleted,
  Change
  FirestoreEvent
} from "firebase-functions/v2/firestore";

export const a = onDocumentWritten("foo/{bar}", (event: FirestoreEvent<Change<DocumentSnapshot>, { bar: string }>) => {});

export const b = onDocumentCreated("foo/{bar}", (event: FirestoreEvent<QueryDocumentSnapshot, { bar: string }>) => {});

export const c = onDocumentUpdated("foo/{bar}", (event: FirestoreEvent<Change<QueryDocumentSnapshot>, { bar: string }>) => {});

export const d = onDocumentDeleted("foo/{bar}", (event: FirestoreEvent<QueryDocumentSnapshot, { bar: string }>) => {});

[taeold]

huh strange that this middle step is needed. Do you know why this is required? (kinda reminds me of TS val as unknown as string trick)

[colerogers]

Firestore is sending the payload as an encoded Any.value, not sure why they chose this, but it was in their original dd

[taeold]

TS Q: I'm not sure why we need Document extends string here. Isn't Document always going to be string anyway?

I see similar pattern in our v1 code (Path extends string) and I'm not sure why that's there too 🤔

[colerogers]

It's used so we can enforce strong typing in our code - https://stackoverflow.com/questions/57342018/extending-a-string-in-typescript

I think Thomas was the one that actually put the Path stuff in during a refactor.

[patrikjuvonen]

This fixed issue #1213