Extend the existing browser/mail default mechanism so users can pick third-party Maps and Calendar apps system-wide.

Update: iOS 18.2 significantly expanded default app support! You can now set defaults for email, messaging, calling, call filtering, browser, passwords, and keyboards. However, Maps and Calendar default apps are still not supported.

Originally requested in 2020 wishlist where browser and mail defaults already existed, but Maps, Calendar, and text editor defaults were still needed.