MOBILE-3947 ion-datetime: Fix timestamp supplied to datetime

ion-datetime no longer uses time zone, it's always UTC now so we had to adapt the initial value supplied. No change needed when reading the value because moment automatically uses the user timezone if the value doesn't specify a timezone.

src/core/services/utils/time.ts

@@ -208,7 +208,11 @@ export class CoreTimeUtilsProvider {
      * @returns Formatted time.
      */
     toDatetimeFormat(timestamp?: number): string {
-        return moment(timestamp || Date.now()).toISOString();
+        const isoString = moment(timestamp || Date.now()).toISOString(true);
+
+        // Remove milliseconds and timezone for consistency with the values used by ion-datetime.
+        // ion-datetime no longer uses timezone, it always uses UTC.
+        return isoString.substring(0, isoString.indexOf('.'));
     }
 
     /**