Difference between Partial objects for `with` and `from_partial`

[nekevss]

When doing some updates on Boa recently, I noticed that there's an important difference between the property bag that is provided to from and with. Namely, with ALWAYS uses the calendar of self where partial. We should update the Partials to account for this difference.

The question is how should this be represented?

My current thoughts is to create a new CalendarFields struct and then PartialDate is updated to:

struct PartialDate {
    calendar_fields: CalendarFields,
    calendar: Calendar,
} 

struct DateTimeFields {
    calendar_fields: CalendarFields,
    time: PartialTime,
}

struct PartialDateTime {
    fields: DateTimeFields,
    calendar: Calendar
}

struct ZonedDateTimeFields {
    calendar_fields: CalendarFields,
    time: PartialTime,
    offset: Offset,
    time_zone: TimeZone,
}

struct PartialZonedDateTime {
    fields: ZonedDateTimeFields,
    calendar: Calendar
}

This would mean that with methods are then updated to accept a XFields struct while from_partial accepts the PartialX.

Of course, this approach ultimately might cause more issues for how ZonedDateTime's from_partial and with_with_provider methods should handle the updates. I've attempted to roughly sketch out the impact of the fields above.

[Manishearth]

This also ties in to #334 : these things need to take in unvalidated Record types.

[nekevss]

Yep, there's a ResolvedCalendarField struct (resolution logic still needs to be improved and may be dependent on the intl-era-month-code proposal). So, the CalendarField would essentially be the public unvalidated record type was the thought.

Note: this also introduces a question of should PartialYearMonth use a special YearMonthCalendarFields or CalendarFields. Granted, that could be resolved by using CalendarFields internally and only exposing with_year (plus era/era_year variants) and with_month(_code)