Add setters for State, StateValues, and FormattedMessage fields for LogRecord.

[Yun-Ting]

Fixes #2877.

For significant contributions please make sure you have completed the following items:

• Appropriate CHANGELOG.md updated for non-trivial changes
• Design discussion issue #
• Changes in public API reviewed

[codecov]

Codecov Report

Merging #2864 (9bb8beb) into main (733c59a) will increase coverage by 0.32%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #2864      +/-   ##
==========================================
+ Coverage   84.91%   85.24%   +0.32%     
==========================================
  Files         259      259              
  Lines        9330     9330              
==========================================
+ Hits         7923     7953      +30     
+ Misses       1407     1377      -30     

Impacted Files	Coverage Δ
src/OpenTelemetry/Logs/LogRecord.cs	96.92% <100.00%> (ø)
...emetry.Api/Internal/OpenTelemetryApiEventSource.cs	76.47% <0.00%> (-2.95%)	⬇️
...metryProtocol/Implementation/ActivityExtensions.cs	92.34% <0.00%> (+3.60%)	⬆️
...tation/OpenTelemetryProtocolExporterEventSource.cs	85.00% <0.00%> (+10.00%)	⬆️
.../OpenTelemetry/Logs/OpenTelemetryLoggerProvider.cs	94.11% <0.00%> (+11.76%)	⬆️
...xporter.OpenTelemetryProtocol/OtlpTraceExporter.cs	77.27% <0.00%> (+40.90%)	⬆️
...entation/ExportClient/OtlpGrpcTraceExportClient.cs	78.57% <0.00%> (+42.85%)	⬆️

[cijothomas]

The change itself might be okay but want to allow sufficient time to fully analyze implications as we are close to 1.2 stable. Blocking to prevent accidental merge.
See https://github.com/open-telemetry/opentelemetry-dotnet/pull/2864/files#r807384255

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