Dataset.File.upload_directory doesn't register a FileDataset

The Dataset.File.upload_directory only uploads the directory, it doesn't register the upload as a file dataset as stated in the documentation. It also doesn't return a registered dataset.

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* ID: 091afd7e-72ca-a384-01db-4da4d40a6734
* Version Independent ID: 0f3783bf-ab1f-f0d6-08f3-90becae914e8
* Content: [azureml.data.dataset_factory.FileDatasetFactory class - Azure Machine Learning Python](https://docs.microsoft.com/en-us/python/api/azureml-core/azureml.data.dataset_factory.filedatasetfactory?view=azure-ml-py#azureml-data-dataset-factory-filedatasetfactory-upload-directory)
* Content Source: [AzureML-Docset/stable/docs-ref-autogen/azureml-core/azureml.data.dataset_factory.FileDatasetFactory.yml](https://github.com/MicrosoftDocs/MachineLearning-Python-pr/blob/live/AzureML-Docset/stable/docs-ref-autogen/azureml-core/azureml.data.dataset_factory.FileDatasetFactory.yml)
* Service: **machine-learning**
* Sub-service: **core**
* GitHub Login: @DebFro
* Microsoft Alias: **debfro**

從 Dataset.File.upload_directory 開始，並將其行為與連結的 FileDatasetFactory 文件和來源 YAML 進行比較。確認目錄上傳如何註冊，以及該方法會回傳什麼；當上傳已註冊為 FileDataset 且回傳已註冊的資料集時，即表示完成。

由索引模型根據 Issue 內容生成。