fix: unpersisted event is handed off into a promise resolution callback

[jstarpl]

The event needs to be persisted before using event.target as that event object can be reused by React by the time the promise resolves.

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[julienw]

Is this a fix for React 16 ?
I see on their website that it's a noop on React 17:

[julienw]

Can you also please share some "steps to reproduce" that would be fixed with your patch?

[julienw]

Alternatively:

Suggested change

	// it's promise, the event needs to be persisted, so that React
	// doesn't reuse the event object while the data function resolves
	event.persist();
	data.then((resp) => {
	showMenuConfig.data = assign({}, resp, {
	target: event.target
	// It's a promise.
	// In React 16, event objects can be reused, therefore it's not safe
	// to use it directly. Let's keep a reference to the target in a local variable.
	const { target } = event;
	data.then((resp) => {
	showMenuConfig.data = assign({}, resp, {
	target

[julienw]

I've left an alternative solution, but I don't mind using yours if you prefer.
Please at least add a reference to React 16 in the comment so that we can remove this code if we remove the support later.