[api] Mark ActivityExtensions.RecordException obsolete

[ysolomchenko]

Fixes #5665

Changes

Mark ActivityExtensions.RecordException obsolete

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
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.27%. Comparing base (6250307) to head (b148505).
Report is 326 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5841      +/-   ##
==========================================
+ Coverage   83.38%   86.27%   +2.89%     
==========================================
  Files         297      257      -40     
  Lines       12531    11185    -1346     
==========================================
- Hits        10449     9650     -799     
+ Misses       2082     1535     -547     

Flag	Coverage Δ
unittests	?
unittests-Project-Experimental	86.20% <100.00%> (?)
unittests-Project-Stable	86.27% <100.00%> (?)

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

Files with missing lines	Coverage Δ
src/OpenTelemetry.Api/Trace/ActivityExtensions.cs	86.36% <100.00%> (-9.10%)	⬇️

... and 226 files with indirect coverage changes