I think maybe we should revert https://github.com/facebook/react/pull/5947.

People already think `proxyEvent` is some kind of an API: https://github.com/facebook/react/issues/12169.

It's also annoying to view in the debugger because none of the properties show up.

Instead, we could seal the event object or something like that.
const isFunction = typeof getVal === 'function';
  return {
    configurable: true,
    set: set,
    get: get,
  };
  function set(val) {