Add occurrence numbering

Author: mmso

test/calendar/recurring.spec.js

@@ -188,11 +188,11 @@ END:VEVENT
 `);
         const cache = {};
         const result = getOccurrencesBetween(component, Date.UTC(2020, 0, 1), Date.UTC(2021, 4, 1), cache);
-        expect(stringifyResultSimple(result)).toEqual([
-            '2020-03-09T03:30:00.000Z - 2020-03-09T05:30:00.000Z',
-            '2020-03-10T03:30:00.000Z - 2020-03-10T05:30:00.000Z',
-            '2020-03-12T03:30:00.000Z - 2020-03-12T05:30:00.000Z',
-            '2020-03-14T03:30:00.000Z - 2020-03-14T05:30:00.000Z'
+        expect(stringifyResult(result)).toEqual([
+            '2020-03-09T03:30:00.000Z - 2020-03-09T05:30:00.000Z | 1',
+            '2020-03-10T03:30:00.000Z - 2020-03-10T05:30:00.000Z | 2',
+            '2020-03-12T03:30:00.000Z - 2020-03-12T05:30:00.000Z | 4',
+            '2020-03-14T03:30:00.000Z - 2020-03-14T05:30:00.000Z | 6'
         ]);
     });