[OneCollectorExporter] Perf improvements

[CodeBlanch]

[These changes were originally part of #1327]

Changes

• Adds the utf8 encoded json to what is stored in the extension cache
• Adds a special case for IReadOnlyList<KeyValuePair<string, object?>> values in json serializer
• Use raw string literals for JSON in tests
• Improves the validation of extension fields to protect against invalid data

TODOs

• Appropriate CHANGELOG.md updated for non-trivial changes
• Unit tests updated

[codecov]

Codecov Report

Merging #1361 (e564839) into main (8ff2bde) will increase coverage by 0.05%.
Report is 4 commits behind head on main.
The diff coverage is 94.44%.

@@            Coverage Diff             @@
##             main    #1361      +/-   ##
==========================================
+ Coverage   73.86%   73.91%   +0.05%     
==========================================
  Files         266      267       +1     
  Lines        9596     9615      +19     
==========================================
+ Hits         7088     7107      +19     
  Misses       2508     2508              

Files Changed	Coverage
...esourceDetectors.Azure/AzureVmMetaDataRequestor.cs	0.00%
...ector/Internal/ExtensionFieldInformationManager.cs	90.90%
...OneCollector/Internal/ExtensionFieldInformation.cs	100.00%
...rialization/CommonSchemaJsonSerializationHelper.cs	100.00%
...erialization/CommonSchemaJsonSerializationState.cs	100.00%