Fix keyboard event handling

Set domKey and domCode property of NativeWebKeyboardEvent. Blink uses
this new interface for keyboard event handling:
https://codereview.chromium.org/2045603002



Task-number: QTBUG-56242
Change-Id: I33f6f17087629f5021874cacd3e75295bbd97870
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>