Implement API surface import with APEX stub

Implement APEX stub of API surface so any stub can be replaced with API
surface when APEX stub interface is required.

Unlike other stub interface, APEX stub can be decided if it should be
used after APEX postdeps mutator analyzes which modules should be
included in which APEX. To cover this, APEX stub is being added to the
dependency if the dependency should not be covered with LLNDK or NDK
stub, and APEX stub exists. From depsToPaths, if dependency to both
original module and API library exists, then it choose one of the
dependency and ignore the other.

To cover this logic, a new property is added to the api_surface :
apex_libs. This is introduced as it is difficult to
gather all api library with apex stub before DepsMutator.

Bug: 264963986
Test: cf_x86_64_phone_vendor build succeeded
Change-Id: I9f0b1f70968e32eba94d3e0d7bb1f4bb29ff2438