Add support for transitive sdk members

Allow an sdk member type to treat some of its dependencies as being
members of the sdk.

Needed for the java_system_modules type whose libs property are an
implementation detail of the system module and so should not be
explicitly listed in the sdk module but still have to be included in
the sdk snapshot.

Bug: 142940300
Test: m nothing
Change-Id: I90f37dae269ef64a6fe9debd0bbaf29a64dd74d8