adbd: add apex_available and visibility for internal libs.

abb links against libadbd_core for the shell protocol, and must be
on the system image because it links against cmd, so let's just
expose it to abb for now.

Exempt-From-Owner-Approval: cherry-pick from AOSP

Bug: http://b/151398197
Test: treehugger
Merged-In: Id926bc4324d3259def21ea19d3bd72320311a6e3
(cherry picked from commit b5673033)
Change-Id: Id926bc4324d3259def21ea19d3bd72320311a6e3