Switch touch input device on hover events.

On a phone in a Mirage headset, two touch nubs are in continuous
contact with the screen while in VR. In order to pass virtual
touchpad events to embedded 2D content that is confined to the
physical display (e.g. permission dialogues), allow a hover event
(as generated for the user's controller pointer) to initiate a
new event.

Bug: 36686408
Test: manual on device
Change-Id: I868472721599843b183b2615aac8e6cd87a58e8e