/// Diagnostic source for warnings and errors reported from explicit build command invocations in Visual Studio.
/// VS workspaces calls into us when a build is invoked or completed in Visual Studio.
/// <see cref="ProjectExternalErrorReporter"/> calls into us to clear reported diagnostics or to report new diagnostics during the build.
/// For each of these callbacks, we create/capture the current <see cref="GetBuildInProgressStateAndToken"/> and
/// For each of these callbacks, we create/capture the current <see cref="BuildInProgressState"/> and
/// schedule updating/processing this state on a serialized <see cref="_taskQueue"/> in the background.
/// The processing phase de-dupes the diagnostics reported from build and intellisense to ensure that the error list does not contain duplicate diagnostics.
/// It raises events about diagnostic updates, which eventually trigger the "Build + Intellisense" and "Build only" error list diagnostic
