[Jaeger] Update preprocessor directives in Jaeger thrift code

[CodeBlanch]

Changes

• Updates preprocessor directives in Jaeger thrift code to be aware of the net6.0 target.

Merge requirement checklist

• CONTRIBUTING guidelines followed (nullable enabled, static analysis, etc.)
• Appropriate CHANGELOG.md files updated for non-trivial changes

[alanwest]

🎉

[codecov]

Codecov Report

Merging #4349 (9b0fdc0) into main (533513f) will increase coverage by 0.04%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4349      +/-   ##
==========================================
+ Coverage   84.66%   84.71%   +0.04%     
==========================================
  Files         298      298              
  Lines       11971    11983      +12     
==========================================
+ Hits        10135    10151      +16     
+ Misses       1836     1832       -4     

Impacted Files	Coverage Δ
...er.Jaeger/ApacheThrift/Protocol/TBinaryProtocol.cs	79.56% <ø> (+0.68%)	⬆️
...r.Jaeger/ApacheThrift/Protocol/TCompactProtocol.cs	79.76% <ø> (+0.49%)	⬆️
...Exporter.Jaeger/ApacheThrift/Protocol/TProtocol.cs	92.15% <ø> (+0.85%)	⬆️

... and 4 files with indirect coverage changes