Memoized components should forward displayName

**Do you want to request a *feature* or report a *bug*?** I'd like to report a bug. **What is the current behavior?** First of all, thanks for the great work on fixing https://github.com/facebook/react/issues/14807. However there is still an issue with the current implementation. `React.memo` does not forward displayName for tests. In snapshots, components display as `<Component />` and string assertions such as `.find('MyMemoizedComponent')` won't work. **What is the expected behavior?** `React.memo` should forward displayName for the test renderer. **Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?** * React 16.8.5 * Jest 24.5.0 * enzyme 3.9.0 * enzyme-adapter-react-16 1.11.2 --- N.B. - Potentially related to https://github.com/facebook/react/issues/14319, but this is related to the more recent changes to support `memo` in the test renderer. Please close if needed, I'm quite new here! I'd be happy to submit a PR if the issue is not too complex to look into :smile: