Investigate double tap zooming on MapViews and SceneViews when JSAPI 4 is released from beta

[jwasilgeo]

We need to verify that 2x-clicking and 2x-tapping to zoom in works for <esri-map-view> and <esri-scene-view> directives, but when JSAPI 4 is released and no longer in beta. That would help isolate the behavior perhaps just to this repo, if it is still an issue after a full JSAPI 4 release. See #211, #235, and also ionic-esri-map's #2 for general background.

[jwasilgeo]

I tested this on a temporary gh-pages fork of this repo. At JSAPI 4.0 this seems to be fine on desktop and mobile, which indicates to me that we needn't worry about the <esri-map-view> and <esri-scene-view> directives for double tap and double click zooming.