Create all variants of stubs for tethering

Add separate publicapi, systemapi and module_libs stubs for tethering.

Bug: 147768409
Test: m
Test: m framework-tethering-stubs-{public,system,module_libs_}api
Change-Id: I0ed44691b4e7080818442a9d0eb37d874f707195
Merged-In: I0ed44691b4e7080818442a9d0eb37d874f707195