iOS 13 adds permission API for device motion

[blairmacintyre]

See the discussion here fartts/superfluity#293

WebXR polyfill is silently printing "No device motion or orientation events will be fired until permission has been requested and granted." to the console, but needs instead to pop up a permission request.

There is no longer a permission setting in Safari's prefs in iOS.

[danrossi]

You can do this in your app. It needs to capture a user click to ask permission and cannot be done while going fullscreen. The notification is underneath the fullscreen element.