Two clients using shared `ClientOptions` class results in duplicate 2-param constructors on each client

The DPG-generated clients have 2 sets of constructors like so:

    public partial class ConversationAnalysisAuthoringClient
    {
        private const string AuthorizationHeader = "Ocp-Apim-Subscription-Key";
        private readonly AzureKeyCredential _keyCredential;
        private const string AuthorizationHeader0 = "Ocp-Apim-Subscription-Key";
        private readonly AzureKeyCredential _keyCredential0;
        private readonly HttpPipeline _pipeline;
        private readonly Uri _endpoint;
        private readonly string _apiVersion;

        /// <summary> The ClientDiagnostics is used to provide tracing support for the client library. </summary>
        internal ClientDiagnostics ClientDiagnostics { get; }

        /// <summary> The HTTP pipeline for sending and receiving REST requests and responses. </summary>
        public virtual HttpPipeline Pipeline => _pipeline;

        /// <summary> Initializes a new instance of ConversationAnalysisAuthoringClient for mocking. </summary>
        protected ConversationAnalysisAuthoringClient()
        {
        }

        /// <summary> Initializes a new instance of ConversationAnalysisAuthoringClient. </summary>
        /// <param name="endpoint"> Supported Cognitive Services endpoint (e.g., https://&lt;resource-name&gt;.api.cognitiveservices.azure.com). </param>
        /// <param name="credential"> A credential used to authenticate to an Azure Service. </param>
        /// <exception cref="ArgumentNullException"> <paramref name="endpoint"/> or <paramref name="credential"/> is null. </exception>
        public ConversationAnalysisAuthoringClient(Uri endpoint, AzureKeyCredential credential) : this(endpoint, credential, new ConversationAnalysisClientOptions())
        {
        }

        /// <summary> Initializes a new instance of ConversationAnalysisAuthoringClient. </summary>
        /// <param name="endpoint"> Supported Cognitive Services endpoint (e.g., https://&lt;resource-name&gt;.api.cognitiveservices.azure.com). </param>
        /// <param name="credential"> A credential used to authenticate to an Azure Service. </param>
        /// <exception cref="ArgumentNullException"> <paramref name="endpoint"/> or <paramref name="credential"/> is null. </exception>
        public ConversationAnalysisAuthoringClient(Uri endpoint, AzureKeyCredential credential) : this(endpoint, credential, new ConversationAnalysisClientOptions())
        {
        }

        /// <summary> Initializes a new instance of ConversationAnalysisAuthoringClient. </summary>
        /// <param name="endpoint"> Supported Cognitive Services endpoint (e.g., https://&lt;resource-name&gt;.api.cognitiveservices.azure.com). </param>
        /// <param name="credential"> A credential used to authenticate to an Azure Service. </param>
        /// <param name="options"> The options for configuring the client. </param>
        /// <exception cref="ArgumentNullException"> <paramref name="endpoint"/> or <paramref name="credential"/> is null. </exception>
        public ConversationAnalysisAuthoringClient(Uri endpoint, AzureKeyCredential credential, ConversationAnalysisClientOptions options)
        {
            Argument.AssertNotNull(endpoint, nameof(endpoint));
            Argument.AssertNotNull(credential, nameof(credential));
            options ??= new ConversationAnalysisClientOptions();

            ClientDiagnostics = new ClientDiagnostics(options, true);
            _keyCredential0 = credential;
            _pipeline = HttpPipelineBuilder.Build(options, Array.Empty<HttpPipelinePolicy>(), new HttpPipelinePolicy[] { new AzureKeyCredentialPolicy(_keyCredential0, AuthorizationHeader0) }, new ResponseClassifier());
            _endpoint = endpoint;
            _apiVersion = options.Version;
        }

        /// <summary> Initializes a new instance of ConversationAnalysisAuthoringClient. </summary>
        /// <param name="endpoint"> Supported Cognitive Services endpoint (e.g., https://&lt;resource-name&gt;.api.cognitiveservices.azure.com). </param>
        /// <param name="credential"> A credential used to authenticate to an Azure Service. </param>
        /// <param name="options"> The options for configuring the client. </param>
        /// <exception cref="ArgumentNullException"> <paramref name="endpoint"/> or <paramref name="credential"/> is null. </exception>
        public ConversationAnalysisAuthoringClient(Uri endpoint, AzureKeyCredential credential, ConversationAnalysisClientOptions options)
        {
            Argument.AssertNotNull(endpoint, nameof(endpoint));
            Argument.AssertNotNull(credential, nameof(credential));
            options ??= new ConversationAnalysisClientOptions();

            ClientDiagnostics = new ClientDiagnostics(options, true);
            _keyCredential0 = credential;
            _pipeline = HttpPipelineBuilder.Build(options, Array.Empty<HttpPipelinePolicy>(), new HttpPipelinePolicy[] { new AzureKeyCredentialPolicy(_keyCredential0, AuthorizationHeader0) }, new ResponseClassifier());
            _endpoint = endpoint;
            _apiVersion = options.Version;
        }

You can also see two sets of authorization headers. This happens when I have an autorest.md file like so:

# Generated code configuration

Run `dotnet build /t:GenerateCode` to generate code.

``` yaml
# The title here is used to generate the single ClientOptions class name.
title: Conversations
license-header: MICROSOFT_MIT_NO_VERSION

input-file:
- https://raw.githubusercontent.com/Azure/azure-rest-api-specs/e7f37e4e43b1d12fd1988fda3ed39624c4b23303/specification/cognitiveservices/data-plane/Language/preview/2022-05-15-preview/analyzeconversations.json
- https://raw.githubusercontent.com/Azure/azure-rest-api-specs/e7f37e4e43b1d12fd1988fda3ed39624c4b23303/specification/cognitiveservices/data-plane/Language/preview/2022-05-15-preview/analyzeconversations-authoring.json

data-plane: true
model-namespace: false
clear-output-folder: true

modelerfour:
  lenient-model-deduplication: true

Customizations

Customizations that should eventually be added to central autorest configuration.

General customizations

Support automatically generating code for key credentials.

directive:
- from: swagger-document
  where: $.securityDefinitions
  transform: |
    $["AzureKey"] = $["apim_key"];
    delete $["apim_key"];

- from: swagger-document
  where: $.security
  transform: |
    $ = [
        {
          "AzureKey": []
        }
    ];
```

This would result in 2 separate client classes by design - a ConversationAnalysisClient and ConversationAnalysisAuthoringClient. Just like we shipped the Question Answering SDK, we want to use 1 ConversationAnalysisClientOptions, so I added a class like so:

    [CodeGenModel("ConversationsClientOptions")]
    public partial class ConversationAnalysisClientOptions : ClientOptions

If I process these input-files in a batch I can probably work around this, but I imagine this wasn’t by design. I also don’t know how the DPG generator came up with ConversationsClientOptions - this isn’t evident from either of the swaggers - but it’s not the name we want. It seems from some minimal testing that this was a big cause of the duplication error.

[annelo-msft]

Thanks for all the effort you put into this, @heaths! Since you are not blocked on this, I have moved the ask to DPG v1.1.

I do think it makes sense to make this easier for DPG library authors 😃

Is it correct to summarize the ask as “Enable generation of a single ClientOptions type for a library”? If so, I will update the title of this issue to reflect that.

[jsquire]

@annelo-msft: Would you please be so kind as to triage?