Create analyzer for test projects that ensures all awaits have a timeout configured

A common cause of unit test hangs are awaiting a task that never completes because of a thread-safety issue. We get around this by calling an extension method that adds a time limit to the await.

https://github.com/aspnet/AspNetCore/blob/49c01eefecf1dbd75e5536aa803d689390c6770a/src/SignalR/clients/csharp/Client/test/UnitTests/HubConnectionTests.Protocol.cs#L78-L88

Instead of awaiting a task forever an exception will be thrown after 5 seconds, the test will fail, and the build will continue.

Today the timeout extension method is added ad-hoc. Someone might be contentious and always add the timeout when writing async code, or they add it later when they encounter a hang when running the tests locally or in CI.

It would be useful to have a Roslyn analyzer for test projects that remind developers to always add timeouts to their tests. ASP.NET Core tests would avoid annoying hangs and run more reliably.