Ensure that displayName is working on ref-forwarded components (for logging purposes)

[shirakaba]

Might be working already, but need to check.

With reference to:

• Get component name in React

May be a case for using a Mixin or decorator.

[shirakaba]

I've witnessed in React Devtools that all ref-forwarding components retain the name of the class they're forwarding to (the name as exported – e.g. _Page – not as imported), even with ref-forwarding involved. The names are similar enough that it's not a problem for me; at least they're not mangled.