Map Stimulus controller filenames to identifiers as in the Stimulus docs

[fpsvogel]

This is a 🐛 bug fix.

I haven't written a test for this change because AFAIK bundled configurations are not included in tests. But let me know if you'd like me to add a test. I did run the tests, though, and none are failing. I also manually tested my changes (more on that below).

Summary

I've made minor changes to the code that the Stimulus bundled configuration adds to index.js, so that Stimulus controllers are detected and named according to the Stimulus docs: https://stimulus.hotwired.dev/handbook/installing#controller-filenames-map-to-identifiers. Specifically, my changes ensure the following:

• If a Stimulus controller has a name longer than one word, and if the words are separated by underscores in the filename, then in the HTML identifier the words are separated by hyphens and not underscores. E.g. reading_list_controller.js gets the identifier reading-list.
• If a Stimulus controller has hyphens instead of underscores in the filename, then the controller is still detected and registered as usual, e.g. reading-list-controller.js.

I manually tested my changes by using the changed JS code in my site's index.js. I ensured that it properly detects and registers Stimulus controllers with long multi-word names, whether the filename is separated by underscores or hyphens.

Context

I noticed this discrepancy with the Stimulus docs when I was building a new site in Bridgetown 1.0 beta. The site has a Stimulus controller called reading_list_controller.js, which was being registered as reading_list, which does not match the reading-list identifier in the HTML.

As I was fixing that, I also noticed that the Stimulus doc linked above allows for hyphen-separated Stimulus controller filenames, so I added that into this PR as well.

This is my very first PR to Bridgetown, so let me know if I've missed anything. Thanks!

[jaredcwhite]

Thanks @fpsvogel, looks good to me!