Replace java.util.concurrent.TimeUnit with java.time.Duration

[Jeff11]

Please add functions that accept Duration for all public functions that currently only accept TimeUnit

For example:
old:
PhoneAuthOptions.Builder(Firebase.auth).setTimeout(60, TimeUnit.SECONDS)

new:
PhoneAuthOptions.Builder(Firebase.auth).setTimeout(Duration.ofSeconds(60))

[google-oss-bot]

I couldn't figure out how to label this issue, so I've labeled it for a human to triage. Hang tight.