Incorrect access of [[HoursValue]] and [[SecondsValue]] of durationFormat in PartitionDurationFormatPattern

[FrankYFTang]

This bug is introduced in #180

There are no [[SecondsValue]] nor [[HoursValue]] defined in
https://tc39.es/proposal-intl-duration-format/#sec-properties-of-intl-durationformat-instances

But in https://tc39.es/proposal-intl-duration-format/#sec-partitiondurationformatpattern
1.1.8 PartitionDurationFormatPattern ( durationFormat, duration )

step 9-j-i-2

2. Let hoursValue be durationFormat.[[HoursValue]].

and step 9-j-i-3-b

b. Let secondsValue be durationFormat.[[SecondsValue]].

this is not implementable.

[FrankYFTang]

@ben-allen @ryzokuken

[FrankYFTang]

@sffc

[ben-allen]

Marking as closed, since this issue is fixed by #188