altKeyOnly = function (mapBrowserEvent) {
  const originalEvent = mapBrowserEvent.originalEvent;
  return (
    originalEvent.altKey &&
    !(originalEvent.metaKey || originalEvent.ctrlKey) &&
    !originalEvent.shiftKey
  );
}
Return `true` if only the alt-key is pressed, `false` otherwise (e.g. when
additionally the shift-key is pressed).

@param {import("../MapBrowserEvent.js").default} mapBrowserEvent Map browser event.
@return {boolean} True if only the alt key is pressed.
@api