Madhus1218 fix csharp generichost oneof serialization

[wing328]

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Summary by cubic

Fixes C# generichost oneOf serialization when no discriminator. Old behavior wrapped everything in an object; new behavior serializes primitives/arrays as raw values and writes referenced model properties inline. This produces correct JSON; discriminator-based serialization is unchanged.

• Review Focus: modules/openapi-generator/src/main/resources/csharp/libraries/generichost/JsonConverter.mustache adds early returns for primitive/array and other non-object oneOf cases, and writes the selected referenced-model properties into the object before common properties. Samples were regenerated across all target frameworks to reflect the corrected output.
• Migration: Regenerate C# generichost clients. Update consumers/tests that depended on object-wrapped JSON for oneOf primitives, arrays/lists, or referenced models.

^{Written for commit 33c9825. Summary will update on new commits.}