added zooming controls to android WebView

### Testing:

To test that pinch zoom and double tap are working, load the example project and use create & show view APIs.

Te test that this can be disabled by meta modify the create API in index.html in the example project to `src: "file:///android_asset/www/customview.html"`.

The customview.html includes `user-scalable=no` which will override the zoom controls.