add integration-tests for language server #118
Description
Using the LanguageClient from https://www.nuget.org/packages/OmniSharp.Extensions.LanguageClient
once we upgrade to at least 0.17.4 we'll be able to use https://www.nuget.org/packages/OmniSharp.Extensions.LanguageProtocol.Testing (see https://github.com/OmniSharp/csharp-language-server-protocol/tree/v0.17.4/src/Testing)