Show that "exports" aliases in package.json cause ES Modules not to be able to import subfolders.

Note, if you're not using the latest version of Node.js, you may need to add the --experimental-modules flag.

The following works, the file imports relative to test-package/dist/ which is specified by value "./": "./dist/" of the "exports" field in test-package/package.json:

node testFooImport.js

The following throws an error wen the file tries to import from test-package/subfolder/, the because the value of "exports" causes the subfolder invisible to the consumer of test-package:

node testBarImport.js

The output is similar to this:

$ node --experimental-modules testFooImport.js 
Foo

$ node --experimental-modules testBarImport.js 
(node:16752) ExperimentalWarning: The ESM module loader is experimental.
internal/modules/esm/default_resolve.js:82
  let url = moduleWrapResolve(specifier, parentURL);
            ^

Error: Cannot find module /home/trusktr/test/node_modules/test-package/dist/subfolder/subfolder/Bar.js imported from /home/trusktr/test/testBarImport.js
    at Loader.resolve [as _resolve] (internal/modules/esm/default_resolve.js:82:13)
    at Loader.resolve (internal/modules/esm/loader.js:73:33)
    at Loader.getModuleJob (internal/modules/esm/loader.js:147:40)
    at ModuleWrap.<anonymous> (internal/modules/esm/module_job.js:41:40)
    at link (internal/modules/esm/module_job.js:40:36) {
  code: 'ERR_MODULE_NOT_FOUND'
}

Related issue: nodejs/node#14970