[otlp] Custom serialzer resource tweaks

[CodeBlanch]

Changes

• Updates ProtobufOtlpResourceSerializer so that it doesn't return OtlpTagWriterState from helper methods. This isn't needed because OtlpTagWriterState is passed in by ref

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.

Project coverage is 86.58%. Comparing base (6250307) to head (e036f52).
Report is 374 commits behind head on main.

Files with missing lines	Patch %	Lines
...ation/Serializer/ProtobufOtlpResourceSerializer.cs	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5947      +/-   ##
==========================================
+ Coverage   83.38%   86.58%   +3.20%     
==========================================
  Files         297      262      -35     
  Lines       12531    11804     -727     
==========================================
- Hits        10449    10221     -228     
+ Misses       2082     1583     -499     

Flag	Coverage Δ
unittests	?
unittests-Project-Experimental	86.56% <66.66%> (?)
unittests-Project-Stable	86.25% <66.66%> (?)

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

Files with missing lines	Coverage Δ
...ation/Serializer/ProtobufOtlpResourceSerializer.cs	88.23% <66.66%> (ø)

... and 243 files with indirect coverage changes

[rajkumar-rangaraj]

Thanks for covering this. I had planned to address it after reviewing your last PR.