Use unsafe relaxed escaping in AIJsonUtilities.DefaultOptions.

[eiriktsarpalis]

It is common for AI vendor APIs to embed JSON documents inside JSON strings, which results in quotes and most non-ASCII content being escaped and confusing consuming LLMs. This updates the default STJ options to use JavaScriptEncoder.UnsafeRelaxedJsonEscaping.

FYI @GrabYourPitchforks@SergeyMenshykh

Microsoft Reviewers: Open in CodeFlow

[dotnet-comment-bot]

‼️Found issues‼️

Project	Coverage Type	Expected	Actual
Microsoft.Extensions.Caching.Hybrid	Line	86	82.77 🔻
Microsoft.Gen.MetadataExtractor	Line	98	57.35 🔻
Microsoft.Gen.MetadataExtractor	Branch	98	62.5 🔻
Microsoft.Extensions.AI.Ollama	Line	80	78.25 🔻

🎉 Good job! The coverage increased 🎉
Update MinCodeCoverage in the project files.

Project	Expected	Actual
Microsoft.Extensions.AI.OpenAI	77	78
Microsoft.Extensions.AI.Abstractions	83	84
Microsoft.Extensions.AI	88	89

Full code coverage report: https://dev.azure.com/dnceng-public/public/_build/results?buildId=943071&view=codecoverage-tab

[dotnet-comment-bot]

‼️Found issues‼️

Project	Coverage Type	Expected	Actual
Microsoft.Extensions.Caching.Hybrid	Line	86	82.77 🔻
Microsoft.Gen.MetadataExtractor	Line	98	57.35 🔻
Microsoft.Gen.MetadataExtractor	Branch	98	62.5 🔻
Microsoft.Extensions.AI.Ollama	Line	80	78.25 🔻

🎉 Good job! The coverage increased 🎉
Update MinCodeCoverage in the project files.

Project	Expected	Actual
Microsoft.Extensions.AI.OpenAI	77	78
Microsoft.Extensions.AI	88	89
Microsoft.Extensions.AI.Abstractions	83	84

Full code coverage report: https://dev.azure.com/dnceng-public/public/_build/results?buildId=943191&view=codecoverage-tab