Editor preview safe zones for notched iPhones do not match those used at runtime

Hi, on iOS we ask the device for its cutout regions, but the values returned by the device can be overridden using the SafeZone.Landscape.* cvars. However these are on-device only settings.

When the UMG and PIE safe zone preview system was added, these variables were not used or updated, and a separate platform-independent r.CustomUnsafeZones cvar was added along with code to read it from the previewed device profile. The default values for r.CustomUnsafeZones for notched iPhones also do not match what the device returns, which is a safe area on the right side screen (opposite the notch when in landscape) and bottom of the screeen for the swipe-to-home area.

We should use r.CustomUnsafeZones on device as well, and the defaults used by the editor preview should match what real devices return.