Log dropped telemetry item count on shutdown

[mic-max]

This feature is important as we want to let users know somehow that we are dropping items.

Changes

• On shutdown, write to an EventSource log with the count of dropped telemetry items since the start
• We may consider writing to the log the current number of dropped items every N drops. In this case, the first item dropped should write and then every subsequent Nth dropped item will write to the log.
  • i.e., The check of this.droppedCount % N == 0 should happen on the line before Interlocked.Increment(ref this.droppedCount);

No dropped items:

Dropped items:

Note: I think the extra space at the end is being added by PerfView?

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Design discussion issue #
• Changes in public API reviewed

[reyang]

Need a changelog entry 😃

[codecov]

Codecov Report

Merging #2331 (c40e300) into main (a538016) will increase coverage by 0.05%.
The diff coverage is 81.81%.

@@            Coverage Diff             @@
##             main    #2331      +/-   ##
==========================================
+ Coverage   79.95%   80.01%   +0.05%     
==========================================
  Files         231      231              
  Lines        7453     7464      +11     
==========================================
+ Hits         5959     5972      +13     
+ Misses       1494     1492       -2     

Impacted Files	Coverage Δ
...nTelemetry/Internal/OpenTelemetrySdkEventSource.cs	71.56% <80.00%> (+0.91%)	⬆️
src/OpenTelemetry/BatchExportProcessor.cs	93.33% <100.00%> (+0.09%)	⬆️
...ter.ZPages/Implementation/ZPagesActivityTracker.cs	100.00% <0.00%> (+2.85%)	⬆️
...emetry.Api/Internal/OpenTelemetryApiEventSource.cs	82.35% <0.00%> (+8.82%)	⬆️

[cijothomas]

I have left a comment about making this more useful for end user.

[reyang]

https://github.com/open-telemetry/opentelemetry-dotnet/pull/2331/files#r707623666

[cijothomas]

@mic-max Looks like changelog has conflicts that must be resolved before we can merge. Can you fix them ?