[TEST] Rename w3c_tracecontext_test to w3c_tracecontext_http_test_server

[psx95]

This rename was requested in PR #3115 to make it more clear that the test artifact being built under ext for w3c trace context compliance is actually a test server.

See this comment requesting this change.

Changes

• Renames the ext/w3c_tracecontext_test directory to ext/w3c_tracecontext_test_server.
• Updates the CI running W3C Trace Context Validation tests to accommodate this rename.

The CMake option has been kept as-is: BUILD_W3CTRACECONTEXT_TEST.

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.83%. Comparing base (497eaf4) to head (ee5e9b9).
Report is 160 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3132      +/-   ##
==========================================
+ Coverage   87.12%   87.83%   +0.71%     
==========================================
  Files         200      195       -5     
  Lines        6109     6136      +27     
==========================================
+ Hits         5322     5389      +67     
+ Misses        787      747      -40     

see 100 files with indirect coverage changes

[marcalff]

LGTM,

with renaming to w3c_tracecontext_http_test_server per @lalitb suggestion.