Normative: Implement optimizations in shared duration rounding code path

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

polyfill/lib/duration.mjs

@@ -27,6 +27,7 @@ import {
 import { TimeDuration } from './timeduration.mjs';
 
 const MathAbs = Math.abs;
+const NumberIsNaN = Number.isNaN;
 const ObjectCreate = Object.create;
 
 export class Duration {
@@ -345,9 +346,7 @@ export class Duration {
         ES.DifferenceZonedDateTimeWithRounding(
           relativeEpochNs,
           targetEpochNs,
-          plainRelativeTo,
           calendarRec,
-          zonedRelativeTo,
           timeZoneRec,
           precalculatedPlainDateTime,
           ObjectCreate(null),
@@ -399,7 +398,7 @@ export class Duration {
       if (ES.IsCalendarUnit(smallestUnit)) {
         throw new RangeError(`a starting point is required for ${smallestUnit}s rounding`);
       }
-      ({ days, norm } = ES.RoundDuration(0, 0, 0, days, norm, roundingIncrement, smallestUnit, roundingMode));
+      ({ days, norm } = ES.RoundTimeDuration(days, norm, roundingIncrement, smallestUnit, roundingMode));
       ({ days, hours, minutes, seconds, milliseconds, microseconds, nanoseconds } = ES.BalanceTimeDuration(
         norm.add24HourDays(days),
         largestUnit
@@ -468,9 +467,7 @@ export class Duration {
       const { total } = ES.DifferenceZonedDateTimeWithRounding(
         relativeEpochNs,
         targetEpochNs,
-        plainRelativeTo,
         calendarRec,
-        zonedRelativeTo,
         timeZoneRec,
         precalculatedPlainDateTime,
         ObjectCreate(null),
@@ -479,6 +476,7 @@ export class Duration {
         unit,
         'trunc'
       );
+      if (NumberIsNaN(total)) throw new Error('assertion failed: total hit unexpected code path');
       return total;
     }
 
@@ -513,6 +511,7 @@ export class Duration {
         unit,
         'trunc'
       );
+      if (NumberIsNaN(total)) throw new Error('assertion failed: total hit unexpected code path');
       return total;
     }
 
@@ -524,7 +523,7 @@ export class Duration {
       throw new RangeError(`a starting point is required for ${unit}s total`);
     }
     norm = norm.add24HourDays(days);
-    const { total } = ES.RoundDuration(0, 0, 0, 0, norm, 1, unit, 'trunc');
+    const { total } = ES.RoundTimeDuration(0, norm, 1, unit, 'trunc');
     return total;
   }
   toString(options = undefined) {
@@ -563,7 +562,7 @@ export class Duration {
         microseconds,
         nanoseconds
       );
-      ({ norm } = ES.RoundDuration(0, 0, 0, 0, norm, increment, unit, roundingMode));
+      ({ norm } = ES.RoundTimeDuration(0, norm, increment, unit, roundingMode));
       let deltaDays;
       ({
         days: deltaDays,