Fix dead references in Context module javadoc

[thswlsqls]

Description

• Context javadoc shows Context.wrapTasks(threadPool) in three examples, but no such method exists — the declared method is taskWrapping, so copying the example does not compile.
• Fixed all three examples to Context.taskWrapping(threadPool). The wrong name dates to Add static wrappers for Executor / ExecutorService using current cont… #2988, which declared taskWrapping but wrote wrapTasks in its example.
• TextMapPropagator#fields javadoc had a stray )} after a closed {@link #inject(...)}; removed it.
• Javadoc-only: no signature or behavior change, so no apidiff or CHANGELOG entry.

Testing done

• ./gradlew :context:check — passed (test + spotlessCheck + ErrorProne/NullAway + jApiCmp).
• No new tests added: docs-only change, test-exempt.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: thswlsqls / name: Eunbin Son (aeea99b)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.77%. Comparing base (824334c) to head (aeea99b).

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #8486      +/-   ##
============================================
- Coverage     78.77%   78.77%   -0.01%     
  Complexity     8579     8579              
============================================
  Files          1009     1009              
  Lines         28993    28993              
  Branches       3599     3599              
============================================
- Hits          22839    22838       -1     
- Misses         5311     5313       +2     
+ Partials        843      842       -1     

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[thswlsqls]

/easycla

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