[sdk-tracing] Allow samplers to set TraceState for propagation-only spans

[CodeBlanch]

Fixes #6054

Changes

• Adjusts the sampler logic so that the TraceStateString may be set when creating propagation-only spans.

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)
• Unit tests added/updated
• Appropriate CHANGELOG.md files updated for non-trivial changes

[rajkumar-rangaraj]

LGTM

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.38%. Comparing base (17bbd83) to head (a473cf6).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6058      +/-   ##
==========================================
- Coverage   86.39%   86.38%   -0.02%     
==========================================
  Files         257      257              
  Lines       11690    11679      -11     
==========================================
- Hits        10100    10089      -11     
  Misses       1590     1590              

Files with missing lines	Coverage Δ
src/OpenTelemetry/Trace/TracerProviderSdk.cs	99.33% <ø> (-0.03%)	⬇️