Embed NOTICE output as an APEX asset.

Instead of outputting an aggregated NOTICE file as an intermediate build
resource to allow Make to include it in the final system-wide NOTICE,
process and embed it as an asset in the final APEX. This allows us to
update the NOTICE contents automatically when an APEX is updated.

Fixes: 135218846
Test: Built mainline modules, apex_test.go
Change-Id: Ic851b330fe93be1f602907d44ecc7886c3b0171b