Use ActivityTraceId/ActivitySpanId for exemplars

[alanwest]

@victlu I think it might make sense to use the .NET ActivityTraceId and ActivitySpanId types on exemplars. Or was your choice of byte[] intentional?

[codecov]

Codecov Report

Merging #2125 (a4ba180) into metrics (95a1367) will increase coverage by 0.05%.
The diff coverage is 0.00%.

@@             Coverage Diff             @@
##           metrics    #2125      +/-   ##
===========================================
+ Coverage    82.96%   83.02%   +0.05%     
===========================================
  Files          211      211              
  Lines         6694     6692       -2     
===========================================
+ Hits          5554     5556       +2     
+ Misses        1140     1136       -4     

Impacted Files	Coverage Δ
src/OpenTelemetry/Metrics/DataPoint/Exemplar.cs	0.00% <0.00%> (ø)
src/OpenTelemetry/Metrics/DataPoint/Exemplar{T}.cs	0.00% <0.00%> (ø)
...emetry.Api/Internal/OpenTelemetryApiEventSource.cs	82.35% <0.00%> (+2.94%)	⬆️
...ZPages/Implementation/ZPagesExporterEventSource.cs	62.50% <0.00%> (+6.25%)	⬆️

[victlu]

@victlu I think it might make sense to use the .NET ActivityTraceId and ActivitySpanId types on exemplars. Or was your choice of byte[] intentional?

I was lazy and just matching bytes type for span_id/trace_id in the OTLP protocol. Having more concrete types is better!