[http-server-csharp] Provide Pattern for user-defined errors

[AlitzelMendez]

issue: #5361

[github-actions]

All changed packages have been documented.

• ✅ @typespec/http-server-csharp

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@typespec/http-server-csharp - feature ✏️

This feature introduces changes to how error models (those using the @error decorator) are handled. Error models will now be represented as classes that extend exceptions, and when one of these custom-defined exceptions is thrown, it will produce HTTP errors as a result.,> ,> The handling of the returned status code will be resolved in the following ways:,> ,> #### If @statusCode is defined, the value of the @statusCode property will be returned,> In this case, 404 will be returned:,> tsp,> @error,> model NotFoundError{,> @statusCode _: 404,> },> ,> ,> ### If @statusCode is not defined, the error 400 will be assigned by default,> In this case, 400 will be returned:,> tsp,> @error,> model NotFoundError{,> statusCode: string;,> },> ,> ,> ### If @min and @max are defined instead of a specific value, the @min value will be returned,> In this case, 500 will be returned:,> ,> tsp,> model Standard5XXResponse {,> @minValue(500),> @maxValue(599),> @statusCode,> statusCode: int32;,> },> ,> ,> ### If @statusCode is defined as a union, the resulting model constructor will require a status code,> In this case, when the model is generated, it will require a status code to be provided:,> tsp,> model Standard4XXResponse {,> @statusCode,> statusCode: 400 | 402;,> },> ,> ,> As a result, the status code must be passed when creating an instance of the model:,> csharp ,> throw new Standard4XXResponse(400);,>

[azure-sdk]

You can try these changes here

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[markcowl]

We need to decide how to handle the request body in the exceptions, both how to generate it and how to customize how to create the request body.

Also need to discuss some end-to-end tests for validation, and what to add to the existing documentation we generate.