Support building for iOS 18

[carson-katri]

Use the camera attribute on RealityView to switch between AR and virtual modes.

<RealityView camera="worldTracking" />
<RealityView camera="virtual" />

The realityViewCameraControls(_:) modifier can be used with the virtual camera mode.

<RealityView camera="virtual" style="realityViewCameraControls(.orbit)" />

Now you can drag to orbit the 3D scene around.

Use the cameraTarget attribute to mark an entity as the target for orbit controls.

<Entity cameraTarget />

Now the camera will automatically reframe to fit this entity as it moves and resizes.