Support for dasherized controller filenames

[adrienpoly]

Summary

This PR extends the current functionality of the Gem to support Stimulus controllers with dasherized names (multi-word-dash_controller.js), in addition to the existing camel_case support (multi_word_controller.js).

Background

The Gem currently supports only Stimulus controllers with names in camel_case.
Dasherized names is part of the Stimulus documentation https://stimulus.hotwired.dev/reference/controllers#identifiers

Given that the controller name written in the DOM is using dash to me it feels more natural to write it like that in my filename.

Changes

This PR adds support for dasherized controller names and includes a corresponding test case. With these changes, the Gem will support the following naming structures:

├── coffee_controller.coffee
├── hello_controller.js
├── multi-word-dash_controller.js
├── multi_word_underscore_controller.js
├── namespace
│   ├── multi-word-dash_controller.js
│   ├── multi_word_underscore_controller.js
│   └── namespaced_controller.js
└── type_script_controller.ts

[marcoroth]

I think this makes sense!

This also aligns with the behavior of the @hotwired/stimulus-webpack-helper npm package