Allow passing the user token to setAuthCookies directly (don't require an Authorization header)

[kmjennison]

Is your feature request related to a problem? Please describe.
Currently, calling setAuthCookies during login requires the Authorization header value to be set to the Firebase ID token. This is limiting. Some people may need to define a custom tokenChangedHandler and pass the token by other means.

Describe the solution you'd like and how you'd implement it
Allow setAuthCookies to take a third optional settings parameter, { token: 'token-here' }. If token is provided, use it; otherwise use the Authorization header value; otherwise throw an error.

Is this a breaking change?
No.

Describe alternatives you've considered
None.

[kmjennison]

Completed in #520.