src/vs/workbench/contrib/preferences/browser/settingsEditor2.ts/createGroupIterator
export function createGroupIterator(group: SettingsTreeGroupElement): Iterable<ITreeElement<SettingsTreeGroupChild>> {
	return Iterable.map(group.children, g => {
		return {
			element: g,
			children: g instanceof SettingsTreeGroupElement ?
				createGroupIterator(g) :
				undefined
		};
	});
}