Add LOCAL_APKCERTS_FILE support.

This is used when Soong and Make don't know the full output file list,
and so use a tool to generate a per-module apkcerts.txt file instead.

Fixes: 160119159
Test: m apkcerts-list
Merged-In: I48183bc8cbf9dcc521f791812734205ed3f28f4c
Change-Id: I48183bc8cbf9dcc521f791812734205ed3f28f4c