--why should also work with node_modules that installed using yarn

[ranyitz]

Currently when using the --why feature we rely on _requiredBy field, provided only by npm.

We should be able to detect if the node_modules were installed by yarn/npm and act accordingly to give a similar experience for both.

We could parse the yarn.lock file, the --why data is being stored there, in a reverse manner, but that should be possible to extract it with some transformations.