firestore: crypto not supported by IE11

[caspergreen]

[REQUIRED] Describe your environment

• Operating System version: Windows
• Browser version: IE11
• Firebase SDK version: 7.13.0, 7.13.1
• Firebase Product: Firestore

[REQUIRED] Describe the problem

Commit a85f81d introduces a call to crypto, which is undefined on IE11, thus throwing an exception.

The fix is to use msCrypto if crypto is undefined, as seen here.

const crypto =
  self.crypto || ((self as unknown) as { msCrypto: Crypto }).msCrypto;

Steps to reproduce:

1. Make a web app that calls firebase.firestore().
2. Open web app from IE11.

Relevant Code:

https://stackblitz.com/edit/firebase-issue-sandbox-wvfegd
A simple call like this will fail (any client configuration will)

  firebase
    .firestore()
    .enablePersistence();

[thebrianchen]

@caspergreen Thanks for reporting a bug! This issue is currently being tracked at #2827, so I'll close this ticket.