Make counters use dedicated thread instead of timer (#25864) (#25978)

Make counters use dedicated thread instead of timer (#25864) (#25978)

* Make a dedicated polling thread for EventCounters

* Cleanup

* remove debug prints

* nit

* Fix comment

* addressing issues from code review

* Fix an assertion from getting fired when we have multiple listeners

* Fix a test issue

* code review feedback

* Fix a potential deadlock

* Fix another deadlock

* Allow s_sleepDurationInMilliseconds to be reset to a larger value

* More issues fix

* Let thread wake up from sleep if needed

* Some suggestions for the counters fix.

The resulting behavior should be the same as what is there now (assuming I didn't mess anything up), these are all just code simplifications that hopefully make it easier to review and maintain going forward. In total I think this reduces the change size in CounterGroup.cs by ~30%.
- With the addition of the AutoResetEvent the ManualResetEvent is no longer needed, removed it.
- Removed the various if foo != null checks for the shared state, it is all initialized once when then thread is created and then assumed to be non-null elsewhere.
- Removed a 2nd lock acquisition inside OnTimer
- Replaced an if with Math.Min in PollForValues

* fix test