Avoid accessing Id on activity start

[vishweshbankwar]

Workaround for:
dotnet/runtime#61857

Changes

In case of legacy activities (i.e. new Activity()), we run the sampler after the activity is started. When the sampler runs it updates the ActivityTraceFlags property based on the sampling result. However, updating the trace flags on activity does not get reflected on Id if the Id was accessed before sampler runs. This results is incorrect propagation when the propagator uses Id property to set the traceparent header. This PR prevents accessing Id before sampler runs by manually creating it using TraceId, SpanId and ActivityTraceFlags.

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

[codecov]

Codecov Report

Merging #2659 (7f86ffe) into main (9e83587) will increase coverage by 0.01%.
The diff coverage is 100.00%.

❗ Current head 7f86ffe differs from pull request most recent head 10f79a7. Consider uploading reports for the commit 10f79a7 to get more accurate results

@@            Coverage Diff             @@
##             main    #2659      +/-   ##
==========================================
+ Coverage   82.89%   82.91%   +0.01%     
==========================================
  Files         249      249              
  Lines        8705     8707       +2     
==========================================
+ Hits         7216     7219       +3     
+ Misses       1489     1488       -1     

Impacted Files	Coverage Δ
...nTelemetry/Internal/OpenTelemetrySdkEventSource.cs	74.76% <100.00%> (+3.33%)	⬆️
...ZPages/Implementation/ZPagesExporterEventSource.cs	56.25% <0.00%> (-6.25%)	⬇️
...Telemetry/Internal/SelfDiagnosticsEventListener.cs	96.87% <0.00%> (-0.79%)	⬇️

[reyang]

Consider using one concat instead of two (might be good to to benchmark and see what's the actual perf/alloc difference).

[vishweshbankwar]

// * Summary *

BenchmarkDotNet=v0.13.1, OS=Windows 10.0.22000
Intel Core i7-8850H CPU 2.60GHz (Coffee Lake), 1 CPU, 12 logical and 6 physical cores
.NET SDK=6.0.100
[Host] : .NET 5.0.12 (5.0.1221.52207), X64 RyuJIT
DefaultJob : .NET 5.0.12 (5.0.1221.52207), X64 RyuJIT

Method	Mean	Error	StdDev
OneConcat	66.48 ns	1.381 ns	2.455 ns
TwoConcat	60.69 ns	1.014 ns	0.792 ns

[vishweshbankwar]

looks like two concat works better.

[reyang]

LGTM.

[reyang]

Might worth a changelog update.

[cijothomas]

@vishweshbankwar Please update the description to explain the impact of the associated issue in the HttpClient/GrpcClient instrumentation or any others using Propagators and leveraging Activity.Id.

We were living with this issue for a loooon time until you found it - so could you open an issue to track improving the unit/functional tests.