Port BasicAddMissingReference.InvokeSomeFixesInVisualBasicThenVerifyReferences to the new test framework

[sharwell]

Roslyn's integration tests use a custom harness, where test code executes in a separate process (testhost.x86.exe or similar) and use .NET Remoting to invoke methods on objects within a Visual Studio instance. This pull request creates a second integration test project using the new test harness from microsoft/vs-extension-testing. In addition to moving maintenance of the test harness infrastructure to a common repository, this change significantly reduces integration test reliance on .NET Remoting in hopes of improving test performance and reliability by executing test code directly within the Visual Studio instance. It also standardizes diagnostics collection (screenshots, Windows event logs, the activity log, and IDE state at point of failure).

This change ports one notoriously flaky test from Roslyn's harness to the new harness, along with its required supporting methods. The new code differs primarily in the following ways:

• Where possible, non-DTE Visual Studio APIs are preferred to DTE APIs
• Where possible, operations are written as asynchronous (this especially includes the test itself, since the test entry point is now the main thread of a Visual Studio instance)
• Since tests run directly within Visual Studio, there is no need to separate in-proc and out-of-proc test objects

The goal of the new test project in the current limited form is twofold:

1. Evaluate the reliability of the test when run under the new harness
2. In the event of failure, compare our ability to diagnose the failure in the new harness with information provided by the old harness

[dibarbet]

iirc there is an async document open service now - https://devdiv.visualstudio.com/DevDiv/_git/VS.RPC.Contracts?path=%2Fsrc%2FMicrosoft.VisualStudio.RpcContracts%2FOpenDocument%2FIOpenDocumentService.cs&_a=contents&version=GBmain

It might more reliably set the focus and there are options to activate it, set selection, set visible ranges, etc.

[sharwell]

I have no idea how one would use this. @olegtk ?