Use asynchronous Go To Definition in VS

**Is your feature request related to a problem? Please describe.**

Currently we implement the synchronous [IGoToDefinitionService](https://sourceroslyn.io/#Microsoft.CodeAnalysis.EditorFeatures/GoToDefinition/IGoToDefinitionService.cs,4878e3bfa8c14358) with [FSharpGoToDefinitionService](https://sourceroslyn.io/#Microsoft.CodeAnalysis.ExternalAccess.FSharp/Internal/Editor/FSharpGoToDefinitionService.cs) which has some potential for locking things up.

**Describe the solution you'd like**

There's an asynchronous interface which should provide a better user experience: [IAsyncGoToDefinitionService](https://sourceroslyn.io/#Microsoft.CodeAnalysis.EditorFeatures/GoToDefinition/IAsyncGoToDefinitionService.cs,1d02a780ba4e2440)

Looks like a good idea to switch to that one.

**Describe alternatives you've considered**

Keep it as it is, because it works fine most of the time.