Temporal: Consistently test that calendar is copied in X.from()

We did this inconsistently in PlainDate and ZonedDateTime, and not in the
other calendar-carrying types. Additionally, we don't have to create the
calendar explicitly in PlainDate.

test/built-ins/Temporal/PlainDate/from/argument-plaindate.js

@@ -8,8 +8,7 @@ includes: [temporalHelpers.js]
 features: [Temporal]
 ---*/
 
-const calendar = new Temporal.Calendar("iso8601");
-const orig = new Temporal.PlainDate(2000, 5, 2, calendar);
+const orig = new Temporal.PlainDate(2000, 5, 2);
 const result = Temporal.PlainDate.from(orig);
 
 TemporalHelpers.assertPlainDate(
@@ -18,11 +17,7 @@ TemporalHelpers.assertPlainDate(
   "PlainDate is copied"
 );
 
-assert.sameValue(
-  result.calendar,
-  calendar,
-  "Calendar is copied"
-);
+assert.sameValue(result.calendar, orig.calendar, "Calendar is copied");
 
 assert.notSameValue(
   result,

test/built-ins/Temporal/PlainDateTime/from/argument-plaindatetime.js

@@ -17,6 +17,8 @@ TemporalHelpers.assertPlainDateTime(
   "PlainDateTime is copied"
 );
 
+assert.sameValue(result.calendar, orig.calendar, "Calendar is copied");
+
 assert.notSameValue(
   result,
   orig,

test/built-ins/Temporal/PlainMonthDay/from/argument-plainmonthday.js

@@ -18,6 +18,8 @@ TemporalHelpers.assertPlainMonthDay(
   /* isoYear = */ 2000
 );
 
+assert.sameValue(result.calendar, orig.calendar, "Calendar is copied");
+
 assert.notSameValue(
   result,
   orig,

test/built-ins/Temporal/PlainYearMonth/from/argument-plainyearmonth.js

@@ -18,6 +18,8 @@ TemporalHelpers.assertPlainYearMonth(
   /* era = */ undefined, /* eraYear = */ undefined, /* isoDay = */ 7
 );
 
+assert.sameValue(result.calendar, orig.calendar, "Calendar is copied");
+
 assert.notSameValue(
   result,
   orig,