Add check if a Plugin is used from an optional reexport

[HannesWell]

Repeating the demand from #2213 (comment)

PDE should given an ERROR (ManifestChecker seems a good place for this) if:

1. A bundle is required with optional
2. This bundle has reexports
3. And this reexported dependencies are not also required by this bundle requiring the other one

Because it can obviously not work to use a reexport through an optional dependency chain and this is really nasty and hard to track.