track static deps when gatherint notices for apex

This change fixes a bug that license info for statically linked
libraries are absent in the merged notice for APEX. The problem was that
we were iterating over the apexFiles list that represents actual files
(not Soong modules) that are included in the APEX. The problem is now
fixed by iterarting the all the modules that directly or indirectly
contribute to the APEX using walkPayloadDeps() function.

Bug: 149455933
Test: m
Change-Id: I38655da62b590b669ab4649815b61a5a8e314154