When using Pen with the ISX, the Phase is always None.

Repro:
1. Download package and project at: https://github.com/Unity-Technologies/InputSystem
2. Open project with 2019.1
3. Open window at: Window -> Input Debugger
4. Select Pen device from the list
5. In the Pen device debugger window, observe the "phase" property while using the pen

Actual: the Phase for pen is stuck at "None"
Expected: The Phase for pen changes as it is used for different inputs.