Implement project load event in preview version of the extension

O# reports when a project is loaded or changed, https://github.com/dotnet/vscode-csharp/blob/eb0d88d29ce06f0f8699aa284948792b2d81adbe/src/observers/TelemetryObserver.ts#L102

We need to add similar functionality for the preview extension, but we'll likely be limiting it to the initial initialization, instead of all project changes.