[Firestore] Typescript error on date

My environment

* Operating System version: macOS Monterey
* Firebase SDK version: 11.2.0
* Firebase Product: Firestore
* Node.js version: v16.17.1
* NPM version: 8.19.2

#### Steps to reproduce:

Just request a document with a timestamp, and get the seconds on the object:

```js
data.entryDate.seconds
```

and I get this typescript error:

```js
Any
Property 'seconds' does not exist on type 'string'.
Translation: You're trying to access seconds on an object that doesn't contain it.
```

Reproduce the issue with Firebase Admin SDK 11.2.0 on Node.js using a Firestore document containing a timestamp, then inspect the inferred type of data.entryDate. Compare the type with the runtime object and verify that accessing data.entryDate.seconds is correctly accepted by TypeScript when the fix is complete.

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