Duration.toJSON() should not print unwanted zeroes

Due to a missing argument, Temporal.Duration.from({ hours: 1 }).toJSON()
would return "PT1H0.0S" instead of "PT1H". The same goes for
toLocaleString() in the absence of Intl.DurationFormat.

No change needed to the spec text or documentation, which are already
correct.

polyfill/lib/duration.mjs

@@ -562,15 +562,15 @@ export class Duration {
   }
   toJSON() {
     if (!ES.IsTemporalDuration(this)) throw new TypeError('invalid receiver');
-    return ES.TemporalDurationToString(this);
+    return ES.TemporalDurationToString(this, 'auto');
   }
   toLocaleString(locales = undefined, options = undefined) {
     if (!ES.IsTemporalDuration(this)) throw new TypeError('invalid receiver');
     if (typeof Intl !== 'undefined' && typeof Intl.DurationFormat !== 'undefined') {
       return new Intl.DurationFormat(locales, options).format(this);
     }
     console.warn('Temporal.Duration.prototype.toLocaleString() requires Intl.DurationFormat.');
-    return ES.TemporalDurationToString(this);
+    return ES.TemporalDurationToString(this, 'auto');
   }
   valueOf() {
     throw new TypeError('use compare() to compare Temporal.Duration');

polyfill/test/duration.mjs

@@ -327,6 +327,12 @@ describe('Duration', () => {
       [{}, () => {}, undefined].forEach((options) => equal(d1.toString(options), 'PT15H23M'));
     });
   });
+  describe('toJSON()', () => {
+    it('is like toString but always with auto precision', () => {
+      const d = Duration.from({ hours: 1 });
+      equal(d.toJSON(), d.toString({ fractionalSecondDigits: 'auto' }));
+    });
+  });
   describe('toLocaleString()', () => {
     it('produces an implementation-defined string', () => {
       const duration = Duration.from({ hours: 12, minutes: 30 });