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.
dispatchConfig,
  targetInst,
  nativeEvent,
  nativeEventTarget,
) {
  if (__DEV__) {
    
    delete this.nativeEvent;
    delete this.preventDefault;
    delete this.stopPropagation;
  }
  this.dispatchConfig = dispatchConfig;
  this._targetInst = targetInst;
  this.nativeEvent = nativeEvent;
  const Interface = this.constructor.Interface;
  for (const propName in Interface) {
    if (!Interface.hasOwnProperty(propName)) {
      continue;