[http-client-csharp] Generated methods trigger AOT warnings

[JonathanCrd]

While working on this PR to migrate a client library, Azure/azure-sdk-for-net#54156, I discovered that the actual output is not AOT safe for certain methods with specific return types, as string[].

We must avoid generating returns with ToObjectFromJson() and use ModelReaderWriter.Read instead.

The problem is in:

typespec/packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/src/Providers/ScmMethodProviderCollection.cs

Lines 369 to 410 in f3d792b

	private ValueExpression GetResultConversion(ClientResponseApi result, HttpResponseApi response, CSharpType responseBodyType, Dictionary<string, ValueExpression> declarations)
	{
	if (responseBodyType.Equals(typeof(BinaryData)))
	{
	return response.Content();
	}
	if (responseBodyType.IsList)
	{
	if (!responseBodyType.Arguments[0].IsFrameworkType || responseBodyType.Arguments[0].Equals(typeof(TimeSpan)) || responseBodyType.Arguments[0].Equals(typeof(BinaryData)))
	{
	return declarations["value"].CastTo(new CSharpType(responseBodyType.OutputType.FrameworkType, responseBodyType.Arguments[0]));
	}
	else
	{
	return response.Content().ToObjectFromJson(responseBodyType.OutputType);
	}
	}
	if (responseBodyType.IsDictionary)
	{
	if (!responseBodyType.Arguments[1].IsFrameworkType || responseBodyType.Arguments[1].Equals(typeof(TimeSpan)) || responseBodyType.Arguments[1].Equals(typeof(BinaryData)))
	{
	return declarations["value"].CastTo(new CSharpType(responseBodyType.OutputType.FrameworkType, responseBodyType.Arguments[0], responseBodyType.Arguments[1]));
	}
	else
	{
	return response.Content().ToObjectFromJson(responseBodyType.OutputType);
	}
	}
	if (responseBodyType.Equals(typeof(string)) && ServiceMethod.Operation.Responses.Any(r => r.IsErrorResponse is false && r.ContentTypes.Contains("text/plain")))
	{
	return response.Content().InvokeToString();
	}
	if (responseBodyType.IsFrameworkType)
	{
	return response.Content().ToObjectFromJson(responseBodyType);
	}
	if (responseBodyType.IsEnum)
	{
	return responseBodyType.ToEnum(response.Content().ToObjectFromJson(responseBodyType.UnderlyingEnumType));
	}
	return result.CastTo(responseBodyType);
	}

The change must be done for the following types:

• List
• Dictionary
• FrameworkType
• Enum

Expected output

We expect:

return ClientResult.FromValue(ModelReaderWriter.Read<IReadOnlyList<string>>(result.GetRawResponse().Content, ModelSerializationExtensions.WireOptions, SampleTypeSpecContext.Default), result.GetRawResponse());

instead of:

return ClientResult.FromValue(result.GetRawResponse().Content.ToObjectFromJson<IReadOnlyList<string>>(), result.GetRawResponse());