Add ComponentSetup to ComponentDeps

Although we don't use the new setup dependency component anywhere yet, I've
replaced all uses of CD.flatDeps with CD.nonSetupDeps. This means that when we
do introduce the setup dependencies, all code in Cabal will still use all
dependencies except the setup dependencies, just like now. In other words,
using the setup dependencies in some places would be a conscious decision; the
default is that we leave the behaviour unchanged.