Generate a better stimulus name for component controller

Using the helper `definitionsFromContext` generate quite long name for
stimulus controller in component, ie :
`tag-list-input-component--tag-list-input`.
This custom loader will generate much more readable name, ie L
`tag-list-input`. It's expecting the following pattern :
ofn_component/ofn_controller.js and will fall back to the default
of replacing "_" by "- and "/" by "--" for controller not matching
the pattern.

app/components/example_component/example_controller.js

@@ -1,4 +1,5 @@
-// This controller will be called "example-component--example", ie "component-subdirectory--js-file-name"
+// This controller will be called "example", ie "js-file-name" minus the "_controller.js"
+// see controller/index.js for more info
 import { Controller } from "stimulus";
 
 export default class extends Controller {}