Demonstration of how to patch the custom element registry to add a `connected` event.

connected-event.js

const originalDefine = CustomElementRegistry.prototype.define;
CustomElementRegistry.prototype.define = function(_name, constructor) {
	const originalConnectedCallback = constructor.prototype.connectedCallback;
	constructor.prototype.connectedCallback = function() {
		// Maybe use a prefixed event name?
		// Maybe configure some options (i.e. whether it bubbles)
		this.dispatchEvent(new CustomEvent("connected"));
		originalConnectedCallback?.call(this, ...arguments);
	}
	originalDefine.call(this, ...arguments);
};