Summary:
If the packager is already watching `/path/to/MyProject`, and it finds symlinks inside `/path/to/MyProject/node_modules` that point to `/path/to/MyProject/path/to/somewhere/else`, there's no need to add the latter to the project roots.
**Test Plan:** replicate an aforementioned project set-up, and verify that only `/path/to/MyProject` is a project root for the packager, while files in `/path/to/MyProject/path/to/somewhere/else` can still be imported so long as they're part of an npm-style package (e.g. `/path/to/MyProject/path/to/somewhere/else/package.json` exists).
Closes https://github.com/facebook/react-native/pull/9819
Differential Revision: D3852591
Pulled By: mkonicek
fbshipit-source-id: 558ab3f835ee3d2bf6174c31595e242992f75601