Proper API hierarchy between MODULE_LIBS and PRIV_APPS system APIs

Test: build / treehugger
Bug: 146727827
Exempt-From-Owner-Approval: Cherry-picking from goog/master to aosp/master
Merged-in: Ia6a1c3a795ceb168f0f478a50e5e2415d6a92ba4
Change-Id: Ia6a1c3a795ceb168f0f478a50e5e2415d6a92ba4