Propagate baggage to the parent context in SpanBuilderShim

[thswlsqls]

Fixes #7677

Description

• When an OpenTracing span builder has an explicit parent (asChildOf / addReference), SpanBuilderShim.start() set the parent Context with only the wrapped parent Span, leaving out the baggage merged from the references.
• As a result, the parentContext the SDK hands to Sampler.shouldSample and SpanProcessor.onStart never carried any baggage, even though the resulting SpanShim did.
• This change computes the merged baggage first and puts it into the parent Context alongside the parent Span.
• Matches what the module already does on the implicit-parent path (SpanShim.storeInContext adds span and baggage to the context) and in Propagation.injectTextMap.
• The no-parent and implicit-parent branches, link handling, and the baggage passed to SpanShim are unchanged.
• Related: OpenTracing Shim: Full multiple parent support. #4916 (introduced merging baggage from all references).

Testing done

• Added SpanBuilderShimTest#baggage_explicitParent_inParentContext: a SpanProcessor captures Baggage.fromContext(parentContext) in onStart; with the fix reverted it fails with expected: "value1" but was: null, with the fix it passes.
• ./gradlew :opentracing-shim:check — 85 tests passed.
• SpanBuilderShim is package-private; no docs/apidiffs change.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.27%. Comparing base (77b1ac4) to head (df38090).

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #8812      +/-   ##
============================================
- Coverage     91.28%   91.27%   -0.02%     
+ Complexity    10528    10526       -2     
============================================
  Files          1008     1008              
  Lines         28465    28466       +1     
  Branches       3617     3617              
============================================
- Hits          25984    25982       -2     
  Misses         1685     1685              
- Partials        796      799       +3     

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Waiting on reviewers · refreshed 2026-09-12 12:36 UTC

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