Normative: Change internal slots of Duration to store mathematical va…

…lues

This changes the internal slots of Duration to store mathematical values
instead of Number values. However, only mathematical values that are (1)
integers, and (2) representable by Number values, are allowed. This is
achieved by storing ℝ(𝔽(_value_)) in the internal slots of Durations and
in the fields of Duration Records.

This should solve the problem of type confusion between Number values and
mathematical values, and eliminate places where operations only defined on
mathematical values (such as abs() and floor()) were applied to the Number
domain.

This is a normative change because it means that it is now impossible for
the Number values NaN, +Infinity, -Infinity, and -0, as well as any
non-integer Number values, and not-exactly-representable Number values
>MAX_SAFE_INTEGER, to be exposed to JS via the property getters of
Temporal.Duration. I suspect this was not possible previously with NaN and
non-integer Numbers, I suspect it may have been possible with infinities
and >MAX_SAFE_INTEGER, and it was definitely possible with -0.

Closes: #1604
Closes: #1715

spec/calendar.html

@@ -798,7 +798,7 @@ <h1>Temporal.Calendar.prototype.dateAdd ( _date_, _duration_ [ , _options_ ] )</
         1. Set _duration_ to ? ToTemporalDuration(_duration_).
         1. Set _options_ to ? GetOptionsObject(_options_).
         1. Let _overflow_ be ? ToTemporalOverflow(_options_).
-        1. Let _balanceResult_ be ! BalanceDuration(_duration_.[[Days]], _duration_.[[Hours]], _duration_.[[Minutes]], _duration_.[[Seconds]], _duration_.[[Milliseconds]], _duration_.[[Microseconds]], _duration_.[[Nanoseconds]], *"day"*).
+        1. Let _balanceResult_ be ? BalanceDuration(_duration_.[[Days]], _duration_.[[Hours]], _duration_.[[Minutes]], _duration_.[[Seconds]], _duration_.[[Milliseconds]], _duration_.[[Microseconds]], _duration_.[[Nanoseconds]], *"day"*).
         1. Let _result_ be ? AddISODate(_date_.[[ISOYear]], _date_.[[ISOMonth]], _date_.[[ISODay]], _duration_.[[Years]], _duration_.[[Months]], _duration_.[[Weeks]], _balanceResult_.[[Days]], _overflow_).
         1. Return ? CreateTemporalDate(_result_.[[Year]], _result_.[[Month]], _result_.[[Day]], _calendar_).
       </emu-alg>