Added basic notification trigger support

[fhasse95]

This PR enhances the local push notification capabilities by introducing scheduled delivery via UNTimeIntervalNotificationTrigger and UNCalendarNotificationTrigger. It focuses on single-event scheduling by evaluating the nextTriggerDate of the specific trigger, providing a solid foundation for timed push notifications while keeping the initial implementation simple by omitting recurring intervals.

To try it out, you can check out the NotificationPlayground in either Skip Showcase or Skip Showcase Fuse.

Related PRs:

• Added support for nextDate and enumerateDates to Calendar skip-foundation#93
• Added basic notification trigger support skip-fuse-ui#88
• Added local notification playground skipapp-showcase#64
• Added local notification playground skipapp-showcase-fuse#45

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