Consider dev-dependencies of non-root packages in some cases

[simolus3]

When constructing a package graph, we only consider regular dependencies for packages that aren't the root package. I think this is fairly reasonable in general (after all, dev-dependencies aren't transitive), but it sometimes makes it counterintuitive as expected builders are not applied.

Consider a buildera writing hidden outputs and b writing to source, assuming that both auto-apply to dependents. b may read the hidden outputs from a. Now, let's say a user has a multi-package project with a root package root and a package dep, where root depends on dep from path.
Now, if root has a dev-dependency on a and b; and dep has a dev-dependency on a, one might assume that hidden files from a are generated for the target in dep. However, they aren't! For me, I was quite surprised to see that b couldn't read expected files in dep and it took me a while to figure out that dep needs a regular dependency for this to work (real-world use case).

Now, I'm wondering if we could loosen up these restrictions a bit. Maybe we can consider dev_dependencies from packages reachable through a path dependency as those typically are part of the same project? Another approach may be to consider dev-dependencies from non-root packages if they are a transitive regular dependency of the root package?

I assume this is a fairly rare scenario so it might not be worth it at all, I'm just wondering if this is worth considering.

[jakemac53]

I don't think we want to try and specialize for this. It would likely cause more confusion than anything I think.

We do have a sort of similar issue here also #3113