Unsure if this should be a final supported format or if we should
support other ways to match instead.

This is a demo to solve the issue hilighted in
https://github.com/erlang/rebar3/pull/1072

Instead fetching and resolving src deps (which could depend on pkg deps)
and then pkg deps this patch combines the two into a single set of
iterations by level. The only difference between src and pkg deps in this
new install_deps is how their deps list is found -- from the config or
lock file for src deps and from the neighbors of the vertex for pkg.

- Crashes in providers lib when no providers in a namespace are bare
- Making sure bareness matches semantics; i.e. a bare provider is
  visible, a non-bare provider is hidden.