Add support for camera zoom levels.

- Cameras can be configured with a zoom level
- When selecting the active camera in a scene:
  - The highest priority camera config will always be used
  - The current zoom level, or nearset lower zoom level camera will break ties (or nearest higher
    zoom if no lower zoom values)
  - The most recently added camera will break remaining ties
- Camera globals/viewer effects can now configure multiple cameras at different zoom levels