[3rd party] Getting current project information

## Environment Data

C# Extension version: 2.0.212

## Issue

For more context this is a follow up issue to [[3rd party] Detecting solution/project changes](https://github.com/dotnet/vscode-csharp/issues/5805)

From a `WorkspaceInformationUpdated` notification an extension was able, in 1.x, to get basic project information like what's available inside `MsBuildWorkspaceInformation`. However this relies on the OmniSharp server and is not available in 2.x (at least not if we want C# Dev Kit to be available).

In 2.x this seems to be handled by the new Roslyn language server but there's no (unless I missed it) way to _talk_ with it from outside the C# extension.

How can another extension stays **in sync** with the C# extension ?