Add ASensor_getHandle API to Sensors NDK

Introduces the ASensor_getHandle API which returns the provided
sensor's internal sensor handle. This allows for AdditionalInfo sensor
events to be mapped to the sensor that generated the event.

Bug: 122366555
Test: Builds, verified function correctly returns sensor's handle
Change-Id: I9a03ccc8b0840481fe1b5b4d1e5bca05adcf48a3