Force an initial event to be sent to ProximitySensor.

When registering a proximity sensor, if the sensor is a
"dual" sensor, and the device starts uncovered, we need to
alert sensor listeners. Prior to this change, we left the
ProximitySensor in an "unknown" state, even though we knew
the device was uncovered.

Add tag to DozeSensor's ProximitySensor

Bug: 194974904
Test: manual && atest SystemUITests
Change-Id: I430cd0d63de9c8f0914d5b0d0ff0d86fc38c0190