[AOT] suppressed trimming warnings in HTTP Instrumentation package

[Yun-Ting]

Towards #3429

cc: @eerhardt, @vitek-karas

Changes

Suppressed trimming warnings IL2026 in HTTP Instrumentation package because the AOT-annotation DynamicallyAccessedMembers
https://learn.microsoft.com/dotnet/api/system.diagnostics.codeanalysis.dynamicallyaccessedmembersattribute?view=net-7.0
in Systm.Net.Http library ensures that top-level properties on the payload object are always preserved.
See https://github.com/dotnet/runtime/blob/f9246538e3d49b90b0e9128d7b1defef57cd6911/src/libraries/System.Net.Http/src/System/Net/Http/DiagnosticsHandler.cs#L325

In .NET runtime repo, there is an API proposal to make payload types in System.Net.Http.DiagnosticsHandler public: dotnet/runtime#82910.
Once .NET runtime makes the above change, OTel should update the HTTP instrumentation implementation to access the public payload types directly.

Merge requirement checklist

• CONTRIBUTING guidelines followed (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

Merging #4770 (8afd865) into main (031ed48) will decrease coverage by 0.03%.
Report is 1 commits behind head on main.
The diff coverage is 88.46%.

❗ Current head 8afd865 differs from pull request most recent head 451554f. Consider uploading reports for the commit 451554f to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4770      +/-   ##
==========================================
- Coverage   82.12%   82.10%   -0.03%     
==========================================
  Files         313      313              
  Lines       12783    12796      +13     
==========================================
+ Hits        10498    10506       +8     
- Misses       2285     2290       +5     

Files Changed	Coverage Δ
...ementation/HttpHandlerMetricsDiagnosticListener.cs	77.14% <85.71%> (+1.38%)	⬆️
...tp/Implementation/HttpHandlerDiagnosticListener.cs	69.60% <89.47%> (+1.17%)	⬆️

... and 3 files with indirect coverage changes

[eerhardt]

LGTM. Thanks!

[CodeBlanch]

LGTM