/// Returns a subsequence, up to the specified maximum length, containing /// the initial elements of the sequence. /// /// If the maximum length exceeds the number of elements in the sequence, /// the result contains all the elements in the sequence. /// /// let numbers = [1, 2, 3, 4, 5] /// print(numbers.prefix(2)) /// // Prints "[1, 2]" /// print(numbers.prefix(10)) /// // Prints "[1, 2, 3, 4, 5]" /// /// - Parameter maxLength: The maximum number of elements to return. /// `maxLength` must be greater than or equal to zero. /// - Returns: A subsequence starting at the beginning of this sequence /// with at most `maxLength` elements. public func prefix(_ maxLength: Int) -> Self.SubSequence