[.NET Analyzer] Warn customers to dispose model types that implement IDisposable

Any model type that wraps a raw network stream (like `BlobClient.DownloadStreaming`) returns a `Response` where `T` implements `IDisposable`. We're not going to make `Response` implement `IDisposable` itself because it's so rarely required. It's harder to notice something needs to be disposed though so we should suggest it with an analyzer.

Start by locating the .NET analyzer entry point and its existing analyzer tests, then inspect the BlobClient.DownloadStreaming Response case described here. Define the expected warning for model types whose T implements IDisposable and add a test showing when disposal should be suggested.

Written by the indexing model from the issue text.