src/vs/workbench/browser/parts/editor/editorActions.ts/OpenNextEditorInGroup/navigate
class OpenNextEditorInGroup:	protected navigate(): IEditorIdentifier {
		const group = this.editorGroupService.activeGroup;
		const editors = group.getEditors(EditorsOrder.SEQUENTIAL);
		const index = group.activeEditor ? editors.indexOf(group.activeEditor) : -1;

		return { editor: index + 1 < editors.length ? editors[index + 1] : editors[0], groupId: group.id };
	}