dillon1000/react

Remove keyMirror in TopLevelTypes (#7597)

This is the last callsite of keyMirror! It removes 0.5k gzipped :)

The only trick with this one is that ReactTestUtils actually iterates over the list of all the events. Instead of duplicating the logic, I used the $Enum feature of flow that lets us statically extract out the type from the dynamic value. Inside of react-dom we're no longer requiring the file directly so it doesn't bloat the file size, and we still get to have static typing, best of both worlds!