- Accessing constructor was confusing and createController is not a core requirement
- Avoid modifying the base Stimulus application class
- Expose `window.StimulusModule` as the module output
- Expose `window.wagtail.app` as the Wagtail Stimulus application instance
- Rename root element variable to `root` in initStimulus (so we do not conflict with potential action option registration that uses `element` variable names)
- Pull in the wagtail.components to the same core.js file and add JSDoc for exposed global
- Relates to #10197
