[repo] Fix conflicts caused by DS upgrade

[CodeBlanch]

It looks like #4959 introduced some assembly conflicts:

https://github.com/open-telemetry/opentelemetry-dotnet/actions/runs/6554128228/job/17800577378#step:5:35

These were not caught by CI!

Phase 1 - Surface issues:

• Set MSBuildTreatWarningsAsErrors to true to surface these issues in CI.

  Update: Seems to have worked: https://github.com/open-telemetry/opentelemetry-dotnet/actions/runs/6578376590/job/17871987060?pr=4967#step:5:225

Phase 2 - Fixes:

• The main fix for the conflict is here: https://github.com/open-telemetry/opentelemetry-dotnet/pull/4967/files#diff-1a3d043822adecb40bb0b87696fa8303d343b91f7027b0ea2987e8e80ae1b0cfR48 bae46cd
• Skip all test projects in pack workflow also fixed some conflicts showing during publish: https://github.com/open-telemetry/opentelemetry-dotnet/pull/4967/files#diff-8b6dee5b66f2c27f1f561c301c0220540023c36de918bdcc06d868fd4733d90aR18
• Turning on MSBuildTreatWarningsAsErrors caused some other issues like package validation workflow was failing with errors on projects with IsPackable = false. Fixed that by using OpenTelemetry.proj instead of the solution for the pack target.
• Some misc cleanup like specifying -p:RunningDotNetPack=true directly instead of using an envvar. The envvar is too easy to miss!

[codecov]

Codecov Report

Merging #4967 (ef6f838) into main (0f58eb1) will increase coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #4967      +/-   ##
==========================================
+ Coverage   83.30%   83.33%   +0.03%     
==========================================
  Files         295      295              
  Lines       12361    12361              
==========================================
+ Hits        10297    10301       +4     
+ Misses       2064     2060       -4     

Flag	Coverage Δ
unittests	83.33% <ø> (+0.03%)	⬆️

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

see 4 files with indirect coverage changes

[utpilla]

Why add this? Did you mean to update the instrumentation libraries CI workflow to use this InstrumentationLibraries.proj file to run tests?

[CodeBlanch]

I updated the workflow to call dotnet test InstrumentationLibraries.proj --framework ${{matrix.version}} but then it fails when some projects don't have a specific target (some libraries don't target net462 for example) so I had to revert it. I left the test targets in InstrumentationLibraries.proj & OpenTelemetry.proj though because I thought it was nice to be able to do dotnet test [project_name].proj on the CLI for local things. But I can remove them if you want they aren't officially being called at the moment. My thinking is basically project files should define at least Restore, Build, and VSTest targets (that's what I'm doing over here on contrib).

[utpilla]

I think it's fine to have them defined.