When the time portion of a duration, rounded relative to a ZonedDateTime,
would land on a non-24-hour day, we'd get incorrect results. This is a
regression from #2508 where although switching the order of
BalanceDateDurationRelative and BalanceTimeDurationRelative was correct,
we should not have removed the MoveRelativeZonedDateTime call.

Closes: #2742

In order to prevent bugs due to discrepancies between two ways of
calculating the same thing such as in #2742, refactor duration rounding
with relativeTo so that

    duration.round({ smallestUnit, largestUnit, relativeTo, ...options })

goes through the same code path and gives the same result as

    const target = relativeTo.add(duration);
    relativeTo.until(target, { smallestUnit, largestUnit, ...options })

but taking into account that the until() methods have a different default
roundingMode than Duration.prototype.round(), and optimizing away as many
user-observable calls as possible.

Similarly,

    duration.total({ unit, relativeTo, ...options })

goes through the same code path, which also returns the total as a
mathematical value if needed.

These optimizations were developed by Adam Shaw:
https://gist.github.com/arshaw/36d3152c21482bcb78ea2c69591b20e0

It does the same thing as previously, although fixes some incidental edge
cases that Adam discovered. However, the algorithm is simpler to explain
and to understand, and also makes fewer calls into user code.

It uses three variations on a bounding technique for rounding: computing
the upper and lower result, and checking which one is closer to the
original duration, and 'nudging' the duration up or down accordingly.

There is one variation for calendar units, one variation for rounding
relative to a ZonedDateTime where smallestUnit is a time unit and
largestUnit is a calendar unit, and one variation for time units.

RoundDuration becomes a lot more simplified, any part of it that was
complex is now split out into the new RoundRelativeDuration and
BubbleRelativeDuration operations, and the three 'nudging' operations.

The operations NormalizedTimeDurationToDays, BalanceTimeDurationRelative,
BalanceDateDurationRelative, MoveRelativeDate, MoveRelativeZonedDateTime,
and AdjustRoundedDurationDays are no longer needed. Their functionality is
subsumed by the new operations.

Closes: #2792
Closes: #2817