[repo] Updates for .NET 9 release

[CodeBlanch]

Changes

• Updates for .NET 9 stable release

Merge requirement checklist

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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.85%. Comparing base (6250307) to head (29b004f).
Report is 385 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5967      +/-   ##
==========================================
+ Coverage   83.38%   86.85%   +3.47%     
==========================================
  Files         297      263      -34     
  Lines       12531    12006     -525     
==========================================
- Hits        10449    10428      -21     
+ Misses       2082     1578     -504     

Flag	Coverage Δ
unittests	?
unittests-Project-Experimental	86.77% <ø> (?)
unittests-Project-Stable	86.77% <ø> (?)
unittests-Solution	86.42% <ø> (?)
unittests-UnstableCoreLibraries-Experimental	85.78% <ø> (?)

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

see 243 files with indirect coverage changes

[CodeBlanch]

@rajkumar-rangaraj This was added here: https://github.com/open-telemetry/opentelemetry-dotnet/pull/5853/files#diff-1788690fb9e80d48d96d92320b51dc391560eb447490867db722279f47939d1eR25-R27

But OTLP doesn't have a dependency on Microsoft.Extensions.Hosting.Abstractions. Seems like a copy/paste issue? I just went ahead and removed it.

[rajkumar-rangaraj]

LGTM

[Falco20019]

This has been a breaking change for us and should not have been on a minor version change according to SemVer2. We rely on 8.x versions of those to ensure we are not breaking upstream customers and this force-updates our dependencies transitively. So please try to avoid those changes without changing the major version in the future.

This also leads to our tooling always suggesting a major-bound update for this library that will break the toolchain, so we have to manually suppress it.