[Tether16] Build Tethering package

Create com.android.tethering apex to pack Tethering.apk and
framework-tethering.jar together.
For go devices, tethering would run in system server process by
InProcessTethering.apk

Bug: 144320246
Test: -build, boot
Change-Id: Id2d68117e99173682908168e99ee28670bd71871