vndk-def: Add --enumerate to deps-closure

This commit adds --enumerate to deps-closure so that a user can print
the dependency closure for each specified libraries or all libraries.

Bug: 62644173
Test: ./vndk_definition_tool.py deps-closure \
--system ... --vendor ...  --enumerate

Change-Id: I18bb27be10c565538356f774cc6752f8cfc79bd4