Hello, we have a TODO for "extend `propagated-inputs` with support for
multiple outputs".  I try to do it for a while, but unable to find a
clear way, since add a new syntax for specify output in
propagated-inputs require changes in too many places..

Think about the intention, what we want is to avoid unwanted
propagated-inputs for building a package or user profiles, and
propagated-inputs is mostly used for development packages which
requiring headers/libraries from its inputs.  It seems I can hardcode
the choice here to the "dev" output (if a package have both "dev" and
"out", its "out" should considered be an application) or the "out"
output (a library/development package).


Then the change is straight: