eslint-import-resolver-typescript fix: resolve modules if folder contains a package.json file

getMappedPath resolves files by trying a number of different file extensions and filtering out those that aren't a file. This does not work when a TSConfig path alias resolves to a directory containing built assets, and described by a package.json, e.g. @foo/bar -> node_modules/foo/bar/dist.

If the tsconfig path is mapped to a folder that doesn't contain an index.${ext} file, then getMappedPath returns undefined as the folder itself is not a file. However, in some cases it is ok for this to resolve to the directory as the package.json contains a typings entry that references a .d.ts file, which is correctly handled by enhanced-resolve.

https://github.com/import-js/eslint-import-resolver-typescript/issues/188