This change adds testable examples for the new Microseconds and Milliseconds methods that were introduced in Go 1.13.

Fixes #34354

Change-Id: Ibdbfd770ca2192f9086f756918325f7327ce0482
GitHub-Last-Rev: 4575f48f5feb8e49742304d17776e28302647931
GitHub-Pull-Request: golang/go#34355
Reviewed-on: https://go-review.googlesource.com/c/go/+/195979Reviewed-by: Alexander Rakoczy <alex@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Alexander Rakoczy <alex@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>