Returns the map style's default camera, if any, or a default camera otherwise. The map style default camera is defined as follows:
center: https://docs.mapbox.com/mapbox-gl-js/style-spec/#root-center
zoom: https://docs.mapbox.com/mapbox-gl-js/style-spec/#root-zoom
bearing: https://docs.mapbox.com/mapbox-gl-js/style-spec/#root-bearing
pitch: https://docs.mapbox.com/mapbox-gl-js/style-spec/#root-pitch
The style default camera is re-evaluated when a new style is loaded.
Returns the map style default camera.