Add Monadic Try construct to the Stainless library

[samuelchassot]

An inline version of the flatMap function works well, but only with Dotty, not scalac.

inline def flatMap[U](inline f: T => Try[U]): Try[U] = this match {
      case Success(t) => f(t)
      case Failure(exc: Exception) => Failure(exc)
    }