Full JsonException type name in DateFormatConverter

[ProductiveRage]

When I was using this to generate C# definitions for the Transifex v3 API (using the JSON from their Download OpenAPI specification link, the generated code was not building because the type JsonException could not be found in the case that it appears within the DateFormatConverter (when SystemTextJson is used).

I changed it to use the full type name (System.Text.Json.JsonException), as seems to be the common use pattern elsewhere, and that seems to have fixed it.

In case it's useful, the settings that I was using were:

var settings = new CSharpClientGeneratorSettings
{
    ClassName = "Transifex{controller}Client",
    CSharpGeneratorSettings =
    {
        Namespace = "TransifexV3.ApiClient",
        GenerateJsonMethods = true,
        GenerateNullableReferenceTypes = true,
        GenerateNativeRecords = true,
        GenerateOptionalPropertiesAsNullable = true,
        ClassStyle = CSharpClassStyle.Record,
        JsonLibrary = CSharpJsonLibrary.SystemTextJson
    },
    GenerateClientInterfaces = true,
    OperationNameGenerator = new MultipleClientsFromPathSegmentsOperationNameGenerator()
};

(Note: There is still an error generating code for the Transifex API when the content type application/vnd.api+json;profile="bulk" is specified because the quotes don't get escaped - but I've raised that as a separate issue)