Ensure a failure to start DTD does not break functionality that does not depend on DTD

See https://github.com/flutter/flutter/issues/151375#issuecomment-2231180224

For now, most of the extension doesn't rely on DTD, so if it fails to start we should alert the user and provide a log, but most functionality should be able to work without it (the same as if using an SDK that doesn't have it).