Use new module for exported sandbox flags

The new module contains the exported flags from
sandbox. The sandbox now has a new library only
for exported flags. The platform code needs to
import this new library in order to access the
exported flags.

Bug: 379770939
Test: New Build && CTS tests && ProcessTest &&
ActivityManagerServiceTest
Flag: EXEMPT Internal Cleanup

Change-Id: I7791f5cad2ff4eba10950fd5b310ba58ea538a2d