This type holds the current state of an F# workspace. It's mutable but thread-safe. It accepts updates to the state and can be queried for information about the workspace. The state can be built up incrementally by adding projects with one of the `Projects.AddOrUpdate` overloads. Updates to any project properties are done the same way. Each project is identified by its project file path and output path or by `FSharpProjectIdentifier`. When the same project is added again, it will be updated with the new information. Project references are discovered automatically as projects are added or updated. Updates to file contents are signaled through the `Files.Open`, `Files.Edit`, and `Files.Close` methods.