This PR updates the `EventCoalescer` to use the `SystemClock` trait to
abstract over the clock.
This allows us to test the advancement of time without relying on the
caller passing in the current time.
Release Notes:
- N/A
When logging the edit environment, we were logging the newest environment being sent into the EventCoalescer on the latest activity log, when we should've been logging the environment that was associated with the ended period within the EventCoalescer.