Expose setUserProperties to set multiple user properties at once

**Is your feature request related to a problem? Please describe.**
There's currently no way to set user properties at once.

**Describe the solution you'd like**
I'd like a `FirebaseAnalytics.setUserProperties({ [name]: [value], ... })` method exposed.

**Describe alternatives you've considered**
The only alternative is to iterate through all the properties and set them one at a time using `FirebaseAnalytics.setUserProperty`. However, this seems inefficient given that the underlying library seems to support `setUserProperties`.