Virtual sensor API.

Add VirtualSensor, VirtualSensorEvent and a callback to notify the sensor owner for any changes in the registered sensor listeners.

The virtual device sensors will registered with the sensor framework as runtime sensors. They must remain valid for the entire lifetime of the virtual device, so they are created when it is created and only unregistered when it is closed. The virtual device owners can access them from the device itself after creation.

This CL is only adding the API, the sensor registration and lifetime management is added in a follow-up CL.

Bug: 237278244
Test: atest VirtualSensorConfigTest
Test: atest VirtualSensorEventTest
Test: atest VirtualDeviceParamsTest
Change-Id: I8bb458dacba1bb65b00e288734ce41186c4fe624