/// This tries to get the FSharpParsingOptions by looking at an internal cache; if it doesn't exist in the cache it will create an inaccurate but usable form of the FSharpParsingOptions.
/// A non-async call that quickly gets the defines of the given F# document.
/// This tries to get the defines by looking at an internal cache; if it doesn't exist in the cache it will create an inaccurate but usable form of the defines.