[otlp] Switch to TagWriter for handling of tags/attributes

[CodeBlanch]

Follow-up to #5476
Relates to #5475

Changes

• Switch from TagTransformer to TagWriter design in OtlpExporter project

Details

See #5475 for information on why this is being done. The TL;DR version is this is set up to write directly onto a stream/buffer and skip all allocations completely (future work). Also there is more utilization of the base class/less duplication of logic in the tag handling for array values inside OtlpExporter code.

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)
• Unit tests added/updated

[codecov]

Codecov Report

Attention: Patch coverage is 98.68421% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 85.72%. Comparing base (6250307) to head (08843e7).
Report is 205 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5585      +/-   ##
==========================================
+ Coverage   83.38%   85.72%   +2.33%     
==========================================
  Files         297      271      -26     
  Lines       12531    11369    -1162     
==========================================
- Hits        10449     9746     -703     
+ Misses       2082     1623     -459     

Flag	Coverage Δ
unittests	?
unittests-Instrumentation-Experimental	87.50% <ø> (?)
unittests-Instrumentation-Stable	87.50% <ø> (?)
unittests-Solution-Experimental	85.73% <98.68%> (?)
unittests-Solution-Stable	85.64% <98.68%> (?)
unittests-Unstable-Core	19.87% <ø> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
...metryProtocol/Implementation/ActivityExtensions.cs	96.13% <100.00%> (+0.20%)	⬆️
...rotocol/Implementation/OtlpLogRecordTransformer.cs	95.32% <100.00%> (+1.86%)	⬆️
...nTelemetryProtocol/Implementation/OtlpTagWriter.cs	100.00% <100.00%> (ø)
...metryProtocol/Implementation/ResourceExtensions.cs	100.00% <100.00%> (ø)
...tryProtocol/Implementation/MetricItemExtensions.cs	91.98% <75.00%> (+9.97%)	⬆️

... and 98 files with indirect coverage changes

[vishweshbankwar]

Curious, why is this changed to TODO?

[CodeBlanch]

The existing TagTransformer<T> we are migrating from doesn't use InvariantCulture today:

opentelemetry-dotnet/src/Shared/TagTransformer.cs

Line 75 in eace49c

var stringValue = TruncateString(Convert.ToString(tag.Value), tagValueMaxLength);

There is a unit test in OtlpExporter which is adding a DateTime.UtcNow as a tag value. With this change to use InvariantCulture that test fails because the format changes.

I discussed a bit with @alanwest. We feel this is a bug. We should be using InvariantCulture in the transformation code. But it is also a breaking change. So the idea was let's do this migration to TagWriter<T> without changing that behavior. Then we can do a dedicated PR/fix for that after the migration so it is independent/clearly documented.