Event Hub Namespace: why specify x-ms-client-flatten for Encryption and Identity

Microsoft.EventHub/preview/2018-01-01-preview/namespaces-preview.json specifies the extension `x-ms-client-flatten` for [`Identity`](https://github.com/Azure/azure-rest-api-specs/blob/03af722477a8ae191de0225cc64fb0acfcf989da/specification/eventhub/resource-manager/Microsoft.EventHub/preview/2018-01-01-preview/namespaces-preview.json#L719) and [`Encryption`](https://github.com/Azure/azure-rest-api-specs/blob/03af722477a8ae191de0225cc64fb0acfcf989da/specification/eventhub/resource-manager/Microsoft.EventHub/preview/2018-01-01-preview/namespaces-preview.json#L745) properties. Why is that? It seems wrong to flatten these properties, and that's not commonly done in other resources.

Also, why is the extension specified on the type and not on the property? It looks like the .NET SDK [ignores](https://github.com/Azure/azure-sdk-for-net/blob/7d4ce1a062fccacc32a550fd5d1eaf5526386958/sdk/eventhub/Microsoft.Azure.Management.EventHub/src/Generated/Models/EHNamespace.cs#L100) the extension. Is this location invalid and should it be ignored?

Start with Microsoft.EventHub/preview/2018-01-01-preview/namespaces-preview.json, inspecting the Identity and Encryption definitions at the linked lines. Compare the extension placement with the linked generated EHNamespace.cs model and similar resources. Done means determining whether the extensions are valid and resolving the spec or documenting the rationale.

Written by the indexing model from the issue text.