Support composer packages that installed outside of vendor directory

[Chi-teck]

The plugin complains on drupal/core package.

I guess that's because the package installed to web/core directory through the composer/installers plugin.

I propose using composer.json file to read installed composer packages.

[Chi-teck]

Also list of installed packages can be found in vendor/composer/installed.json file.

[Chi-teck]

Tried additionalPackagesRoot: ./web/core with no success.