Inconsistent Path Processing

The `paths` argument in `FullRepoManager` supposedly take a collection of paths relative to the `repo_root_dir`, however, when using the `FullyQualifiedNameProvider`, the `gen_cache` function calls the `libcst.helpers.module.calculate_module_and_package`, which then calls `relative_to` function on the already relative paths. This raises the ValueError saying that path X is not a subpath of path Y.
I have checked and the only two places this helper function is used are in the context of `FullRepoManager`, so I think it would be safe to remove the `relative_to` in `libcst.helpers.module.calculate_module_and_package`.