Allow different approximations in the observational Islamic calendar

The "islamic" calendar id refers to the observational Islamic calendar
and different implementation may use different algorithms to approximate
when the moon's crescent can be observed. Change the test data to allow
the approximations used in ICU4X in addition to the ones used in ICU4C.

Additionally allow implementations to canonicalise the calendar id.

test/staging/Intl402/Temporal/old/islamic-calendars.js

@@ -12,12 +12,27 @@ features: [Temporal]
 const tests = [
   {
     calendar: "islamic",
-    inLeapYear: false,
-    daysInYear: 354,
-    daysInMonth12: 29,
-    isoYear: 2023,
-    isoMonth: 7,
-    isoDay: 18
+    choices: [
+      // Approximations of the observational Islamic calendar as computed by ICU4C.
+      {
+        inLeapYear: false,
+        daysInYear: 354,
+        daysInMonth12: 29,
+        isoYear: 2023,
+        isoMonth: 7,
+        isoDay: 18
+      },
+
+      // Approximations of the observational Islamic calendar as computed by ICU4X.
+      {
+        inLeapYear: true,
+        daysInYear: 355,
+        daysInMonth12: 30,
+        isoYear: 2023,
+        isoMonth: 7,
+        isoDay: 19
+      }
+    ],
   },
   {
     calendar: "islamic-umalqura",
@@ -48,12 +63,27 @@ const tests = [
   },
   {
     calendar: "islamic-rgsa",
-    inLeapYear: false,
-    daysInYear: 354,
-    daysInMonth12: 29,
-    isoYear: 2023,
-    isoMonth: 7,
-    isoDay: 18
+    choices: [
+      // Approximations of the observational Islamic calendar as computed by ICU4C.
+      {
+        inLeapYear: false,
+        daysInYear: 354,
+        daysInMonth12: 29,
+        isoYear: 2023,
+        isoMonth: 7,
+        isoDay: 18
+      },
+
+      // Approximations of the observational Islamic calendar as computed by ICU4X.
+      {
+        inLeapYear: true,
+        daysInYear: 355,
+        daysInMonth12: 30,
+        isoYear: 2023,
+        isoMonth: 7,
+        isoDay: 19
+      }
+    ],
   },
   {
     calendar: "islamic-tbla",
@@ -67,15 +97,29 @@ const tests = [
 ];
 
 for (const test of tests) {
-  const { calendar, inLeapYear, daysInYear, daysInMonth12, isoYear, isoMonth, isoDay } = test;
+  const { calendar, choices = [test] } = test;
   const year = 1445;
   const date = Temporal.PlainDate.from({ year, month: 1, day: 1, calendar });
   const isoFields = date.getISOFields();
-  assert.sameValue(date.calendarId, calendar);
+  if (calendar !== "islamicc") {
+    assert.sameValue(date.calendarId, calendar);
+  } else {
+    // TODO: Steps to canonicalize the calendar identifier are still missing.
+    // https://github.com/tc39/ecma402/issues/828
+  }
   assert.sameValue(date.year, year);
   assert.sameValue(date.month, 1);
   assert.sameValue(date.monthCode, "M01");
   assert.sameValue(date.day, 1);
+
+  // Match the possible choice by comparing the ISO month and day values.
+  const choice = choices.find(({ isoMonth, isoDay }) => {
+    return isoFields.isoMonth === isoMonth && isoFields.isoDay === isoDay;
+  });
+  assert(choice !== undefined, `No applicable choice found for calendar: ${calendar}`);
+
+  const { inLeapYear, daysInYear, daysInMonth12, isoYear, isoMonth, isoDay } = choice;
+
   assert.sameValue(date.inLeapYear, inLeapYear);
   assert.sameValue(date.daysInYear, daysInYear);
   assert.sameValue(date.monthsInYear, 12);