Hey - thanks a lot for this polyfill !

I run into a situation where elements that have a formAssociated = true , but do not call attachInternals in their constructor.

For example: https://github.com/material-components/material-web/blob/c3d303eaac1e38e48ea138e0eec034bffdc84c4b/button/internal/button.ts#L42

The polyfill breaks when those elements are attached to the DOM and call upgradeInternals :

	const upgradeInternals = (ref) => {
			if (ref.constructor['formAssociated']) {
					const internals = internalsMap.get(ref);
					const { labels, form } = internals;
					initLabels(ref, labels);
					initForm(ref, form, internals);
			}
	};

as internals is undefined in this case, the app throws with:
Uncaught TypeError: Cannot destructure property 'labels' of 'internals' as it is undefined.

Those elements are then not rendered.