Reference code has mixed-sign duration errors in some non-ISO calendar difference computations

[ptomato]

Reproducers:

const calendar = 'chinese';
const a = new Temporal.PlainDate(2016, 7, 31, calendar);
const b = new Temporal.PlainDate(2017, 7, 31, calendar);
b.since(a, { largestUnit: 'years' });

const calendar = 'hebrew';
const a = new Temporal.PlainDate(1967, 2, 28, calendar);
const b = new Temporal.PlainDate(1968, 3, 1, calendar);
a.until(b, { largestUnit: 'years' });

Crashes with:

file:///.../proposal-temporal/polyfill/lib/ecmascript.mjs:2859
      if (sign !== 0 && propSign !== sign) throw new RangeErrorCtor('mixed-sign values not allowed as duration fields');
                                                 ^

RangeError: mixed-sign values not allowed as duration fields
    at Module.RejectDuration (file:///.../proposal-temporal/polyfill/lib/ecmascript.mjs:2859:50)
    at new Duration (file:///.../proposal-temporal/polyfill/lib/duration.mjs:68:8)
    at TemporalDurationFromInternal (file:///.../proposal-temporal/polyfill/lib/ecmascript.mjs:3009:10)
    at Module.DifferenceTemporalPlainDate (file:///.../proposal-temporal/polyfill/lib/ecmascript.mjs:3769:16)

I haven't investigated these, except to check that they are not regressions from #3156. I'm opening this issue so I don't forget to investigate this at some later time.

[catamorphism]

It seems like the bug is here: https://github.com/tc39/proposal-temporal/blob/main/polyfill/lib/calendar.mjs#L1068

        const intermediate =
          years || months ? this.addCalendar(calendarOne, { years, months }, 'constrain', cache) : calendarOne;

In this case, a year gets subtracted from calendarOne, but that's a 384-day year since calendarOne is in a leap year, and then remainingDays is the wrong sign because the actual difference between the two dates is 365 days.

I'm not sure what the fix should be, though.

[ptomato]

Fixed by #3176.