Add a fake step counter sensor HAL

This is done by extending the original sensor HAL for Cuttlefish.

Bug: 124355112
Test: $ lunch aosp_cf_x86_64_gsi-userdebug
      $ m -j32
      $ find $OUT/vendor -name *stepcounter.xml # It exists.
      # Launch the built image
      $ atest DeviceHealthTests:com.android.devicehealth.tests.SensorsBootCheck

Change-Id: Ia440cc306ac2aefff59187ecb7c396069ad2d6d8