Add a NuGet.Config to stabilize tests

Extract MessageFilter to a top level test utility class

Code cleanup in VisualStudioInstanceFactory found during integration test work

Move IntegrationService (used by integration tests) to its own project

This change ensures tests stay on the main thread, which has the COM message
filter installed that deals with certain IPC delays. DTE operations from
other threads are not able to gracefully recover from certain failure
conditions.

This improves the performance of integration tests by reducing the amount of time
it takes to restart a Visual Studio instance.

This change prevents the customized NuGet.Config from the Roslyn repository from
being used by Visual Studio when integration tests are running in CI builds.

Add feature to allow converting from a tuple to a named-struct.

Merge dev15.9.x to master

Convert to AsyncPackage

Transfer leading trivia in ChangeSignature

Initial impl of 'convert anonymous type to tuple' refactoring

Update project files to not references C# or VB.

Fix VB snippet tests race condition