Make DozeSensors, DozeTriggers use ProximitySensor

This CL takes the features used in DozeSensors and applies
them to the publicly available util.sensors.ProximitySensor class.

It introduces a RateLimiter class for temprorarily suspending the
ProximitySensor as requested.

It introduces a ProximityCheck class for a quick, one time test
of the proximity sensor.

There is some reshuffling of Sensor related code to its own package
as well.

Bug: 141122220
Test: atest SystemUITests
Change-Id: If126be9a56c6966c1678ee70fa6f4623e51361a7