Editorial: Change TimeDuration to use time durations instead of internal durations

[anba]

Changes:

• Move handling for day units from RoundTimeDuration to Temporal.Duration.prototype.round.
• Correct argument type for DifferenceInstant to only allow time units.
• RoundTimeDuration is now only called with time units and its input and output is a time duration.
• Remove the no rounding fast path from DifferenceTemporalPlainTime to match DifferenceInstant.

Fixes:
TemporalDurationFromInternal is fallible in Temporal.Duration.prototype.toString:

Temporal.Duration.from({
  days: 1,
  seconds: 2**53 - 1 - (24*60*60),
  nanoseconds: 999_999_999
}).toString({
  roundingMode: "ceil",
  fractionalSecondDigits: 7
});

[ptomato]

Thanks! I made the corresponding changes in the reference code. We should add test262 coverage for the case you identified, but I'll open a separate issue for that.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.97%. Comparing base (99f67ee) to head (c957836).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3026   +/-   ##
=======================================
  Coverage   95.96%   95.97%           
=======================================
  Files          21       21           
  Lines        9677     9684    +7     
  Branches     1746     1745    -1     
=======================================
+ Hits         9287     9294    +7     
  Misses        337      337           
  Partials       53       53           

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