Documentation: Firebase documentation is not mentioning error code `auth/requires-recent-login` for `verifyBeforeUpdateEmail`

# Describe your environment

* Operating System version: OSX Big Sur 11.2.3
* Browser version: Chrome Version 91.0.4472.164 (Official Build) (x86_64)
* Firebase SDK version: `"firebase": "^8.2.4"`
* Firebase Product: Documentation

# Describe the problem

Firebase documentation is not mentioning error code `auth/requires-recent-login` for `verifyBeforeUpdateEmail` and does not mention `verifyBeforeUpdateEmail` being a sensitive operation.

Link to docs:
https://firebase.google.com/docs/reference/js/firebase.User#verifybeforeupdateemail

#### Steps to reproduce:

- Authenticate with firebase (Email/password)
- Wait until you're not longer recently authenticated.
- Run `firebase.auth().currentUser.verifyBeforeUpdateEmail(email)`
- Error.code is `auth/requires-recent-login`

#### Relevant Code:

```javascript
firebase
.auth()
.currentUser.verifyBeforeUpdateEmail(email)
.then(() => {
// success
})
.catch(error => {
// error.code 'auth/requires-recent-login'
});
```


Open the linked Firebase User reference for verifyBeforeUpdateEmail and compare its documented errors and operation guidance with the reported behavior. Confirm the page explains auth/requires-recent-login and identifies the method as a sensitive operation; the documentation is done when both details are present and accurate.

Written by the indexing model from the issue text.