Indicate sensor discontinuity via SensorEvent

Use a bool in SensorEvent rather than a new method in
SensorEventCallback to indicate discontinuities.

Fixes: 217364461
Test: additional CTS test cases pending
CTS-Coverage-Bug: 214618172
Change-Id: I144487d36b2d00d57265c9e3e9f542c7136a33f5
4 files changed