Use propagated clock in RtcEventLog unittests

* Provide clock to EventGenerator and use it thus no longer rely on
RtcEvent constructor to populate the timestamp.
* Relax expectation of the log time to be within 1 ms instead of that it rounds to ms in a specific way.
* For all log times (except utc time) use non-global SimulcatedClock
instead of global FakeClock
* Providing clock to the RtcEventLog
implementation through Environment,
* while at it, switch to CreateTestEnvironment. In particular that helper has simpler api for providing field trials keeping the same test functionality

Bug: webrtc:42223992
Change-Id: I1c8184143b1ef1736c66af526c88065a26f36b77
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/419540
Reviewed-by: Björn Terelius <terelius@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#46018}