Copy shared_libs and system_shared_libs to module snapshot

This change ensures that the runtime dependencies between a
binary/shared library are correctly specified in the snapshot so that
the build can ensure that shared libraries are built before the targets
that use them.

It adds support for differentiating between references that are
required to refer to another sdk member (required) and those that may
refer to either an sdk member or a non-sdk member (optional). The
latter is used for shared library references as the libraries used by
an sdk member may be provided from outside the sdk. e.g. liblog is not
part of the ART module but is used by some members of the ART sdk.

Bug: 142935992
Test: m nothing
Change-Id: Ia8509ffe79b208c23beba1880fe9c8a92b732685