建立一個空的MapView

1. 使用satellite，除了地形圖，沒有多餘的文字。
2. 建一個MKTileOverlay，利用canReplaceMapContent隱藏地圖。

var mapView: MKMapView = {
    let view = MKMapView()
    view.mapType = .satellite
    view.delegate = self
    
    let overlay = MKTileOverlay()
    overlay.canReplaceMapContent = true
    view.addOverlay(overlay)
    
    return view
}()

PS. 記得重畫MKTileOverlay

extension ContentViewController: MKMapViewDelegate {
   func mapView(_ mapView: MKMapView, rendererFor overlay: MKOverlay) -> MKOverlayRenderer {
        return MKOverlayRenderer(overlay: overlay)
   }
}