Add support for head-tracker sensor type and reference reset

Pose listeners can now be notified whenever the received pose has a
different frame of reference than previous samples and this results in
a recenter.

In addition, the private sensor type used for head tracking is now
supported.


Test: Manual verification using uhid-sample
Bug: 188502620
Change-Id: Ibe86e654656b2797ecc6fc936769e1148d9e02fd