We should not enumerate files excluded in packExclude

[rustd]

We enumerate folders in packExclude. This breaks when we try to enumerate node_modules folder since the file path can be long due to the deep nesting structure of node_modules

Repro steps

1. Create a starter web.
2. Delete the node_module
3. Close the App.
4. Reopen the app to force a restore. This will restore the node_module folder.
5. Do Kpm pack and you will run into the following exception

System.IO.PathTooLongException: The specified path, file name, or both are too long. The fully qualified file name must
be less than 260 characters, and the directory name must be less than 248 characters.