Add support to React DevTools for react-events

[bvaughn]

This could mean a lot of things, longer term, but for the short term I think we need a way to uniquely identify types of EventComponent (something akin to the displayName attribute that custom components support). The information currently available on the Fiber type doesn't provide that.

As for EventTarget types, I see we have a unique symbol for the touch hit type (the only current target type?)- do we plan to add more unique symbols for future target types? If so, this would be sufficient to identify these.

[trueadm]

EventTarget can indeed have more types, but there's only one right now – plus the user can create their own. I have a PR up that adds these fields to both objects: #15268.

[necolas]

Closing as we're no longer developing the Flare API. See #15257 (comment)