[repo] Update the System.Diagnostics.DiagnosticSource and Microsoft.Extensions.* packages to .NET 9.0 RC.1

[rajkumar-rangaraj]

Fixes #5846

Changes

Please provide a brief description of the changes here.

• Updated the System.Diagnostics.DiagnosticSource and Microsoft.Extensions.* packages to .NET 9.0 RC.1
• Updated System.Text.Json to 9.0.0-rc.1.24431.7 for tests and examples
• Updated RELEASENOTES.md

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 86.34%. Comparing base (6250307) to head (c6b9d22).
Report is 321 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5853      +/-   ##
==========================================
+ Coverage   83.38%   86.34%   +2.95%     
==========================================
  Files         297      257      -40     
  Lines       12531    11168    -1363     
==========================================
- Hits        10449     9643     -806     
+ Misses       2082     1525     -557     

Flag	Coverage Δ
unittests	?
unittests-Project-Experimental	86.18% <ø> (?)
unittests-Project-Stable	85.96% <ø> (?)
unittests-Solution	86.31% <ø> (?)
unittests-UnstableCoreLibraries-Experimental	85.60% <ø> (?)

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see 223 files with indirect coverage changes