Normative: Fix ambiguity in FractionalPart grammar

In ParseISODateTime, where the algorithm refers to "the part of
_isoString_ produced by the |TimeFractionalPart| production", it is
ambiguous whether this means the fractional part of the seconds in the
time representation, or the fractional part of the seconds in the
UTC-offset-named time zone.

That is, in the following string,
2021-09-01T02:03:04.56789+23:12:07.987654321[+11:22:33.444445555]
it could refer to "56789" or "444445555"

This fixes the ambiguity by eliminating TimeFractionalPart and referencing
TimeFraction wherever TimeFractionalPart was previously referenced. Note
that TimeFraction includes the decimal separator as well, where
TimeFractionalPart did not, so string indices have to increase by one.

Closes: #1794

Author: ptomato

spec/abstractops.html

@@ -825,11 +825,8 @@ <h1>ISO 8601 grammar</h1>
       FractionalPart :
           DecimalDigit DecimalDigit? DecimalDigit? DecimalDigit? DecimalDigit? DecimalDigit? DecimalDigit? DecimalDigit? DecimalDigit?
 
-      TimeFractionalPart :
-          FractionalPart
-
       Fraction :
-          DecimalSeparator TimeFractionalPart
+          DecimalSeparator FractionalPart
 
       TimeFraction :
           Fraction
@@ -1071,7 +1068,7 @@ <h1>ParseISODateTime ( _isoString_ )</h1>
     <emu-note>The value of ? ToIntegerOrInfinity(*undefined*) is 0.</emu-note>
     <emu-alg>
       1. Assert: Type(_isoString_) is String.
-      1. Let _year_, _month_, _day_, _hour_, _minute_, _second_, _fraction_, and _calendar_ be the parts of _isoString_ produced respectively by the |DateYear|, |DateMonth|, |DateDay|, |TimeHour|, |TimeMinute|, |TimeSecond|, |TimeFractionalPart|, and |CalendarName| productions, or *undefined* if not present.
+      1. Let _year_, _month_, _day_, _hour_, _minute_, _second_, _fraction_, and _calendar_ be the parts of _isoString_ produced respectively by the |DateYear|, |DateMonth|, |DateDay|, |TimeHour|, |TimeMinute|, |TimeSecond|, |TimeFraction|, and |CalendarName| productions, or *undefined* if not present.
       1. If the first code unit of _year_ is 0x2212 (MINUS SIGN), replace it with the code unit 0x002D (HYPHEN-MINUS).
       1. Set _year_ to ! ToIntegerOrInfinity(_year_).
       1. If _month_ is *undefined*, then
@@ -1089,11 +1086,11 @@ <h1>ParseISODateTime ( _isoString_ )</h1>
         1. Set _second_ to 59.
       1. If _fraction_ is not *undefined*, then
         1. Set _fraction_ to the string-concatenation of the previous value of _fraction_ and the string *"000000000"*.
-        1. Let _millisecond_ be the String value equal to the substring of _fraction_ from 0 to 3.
+        1. Let _millisecond_ be the String value equal to the substring of _fraction_ from 1 to 4.
         1. Set _millisecond_ to ! ToIntegerOrInfinity(_millisecond_).
-        1. Let _microsecond_ be the String value equal to the substring of _fraction_ from 3 to 6.
+        1. Let _microsecond_ be the String value equal to the substring of _fraction_ from 4 to 7.
         1. Set _microsecond_ to ! ToIntegerOrInfinity(_microsecond_).
-        1. Let _nanosecond_ be the String value equal to the substring of _fraction_ from 6 to 9.
+        1. Let _nanosecond_ be the String value equal to the substring of _fraction_ from 7 to 10.
         1. Set _nanosecond_ to ! ToIntegerOrInfinity(_nanosecond_).
       1. Else,
         1. Let _millisecond_ be 0.