Dynamic URLs in JS don't get rewritten (rootURL case)

```js
class Foo {
imagePath = `${imageDir}/sample.png`;
}
```

This doesn't get rewritten with the asset rev. One use case for this is in an Ember app that specifies a rootURL. Because a JS declaration to a path doesn't handle rootURLs, we have to prefix them with `${ENV.rootURL}/assets/images/sample.png`.

Start by reproducing the JavaScript snippet from the issue in broccoli-asset-rev, including the Ember app rootURL case. Trace how the plugin detects asset paths and applies fingerprinting, then verify that the dynamic image path is rewritten correctly without breaking rootURL handling.

Written by the indexing model from the issue text.