Fix observable call of ToTemporalTimeZone in ToTemporalZonedDateTime

The reference code was out of line with the spec text here, which says
that ToTemporalTimeZone must be called before
InterpretTemporalDateTimeFields. Both calls are observable.

See also tc39/proposal-temporal#2252

UPSTREAM_COMMIT=a00d9593b807b58c3176570e64ad7b8e0eb4f22b

Author: ptomato

lib/ecmascript.ts

@@ -1770,12 +1770,12 @@ export function ToTemporalZonedDateTime(
     ] as const);
     const fieldNamesWithTzAndOffset = ArrayPush(fieldNames, 'timeZone', 'offset');
     const fields = PrepareTemporalFields(item, fieldNamesWithTzAndOffset, ['timeZone']);
+    timeZone = ToTemporalTimeZone(fields.timeZone);
     ({ year, month, day, hour, minute, second, millisecond, microsecond, nanosecond } = InterpretTemporalDateTimeFields(
       calendar,
       fields,
       options
     ));
-    timeZone = ToTemporalTimeZone(fields.timeZone);
     offset = fields.offset;
     if (offset === undefined) {
       offsetBehaviour = 'wall';