Circular import breaks building with Google Closure Compiler

[Jannis]

There is a circular dependency between type/definition.js and type/wrappers.js, which breaks building graphql-js with the Google Closure Compiler (which has no solution to breaking circular imports yet, see this issue).

The affected code is located here:

https://github.com/graphql/graphql-js/blob/master/src/type/definition.js#L35

and

https://github.com/graphql/graphql-js/blob/master/src/type/wrappers.js#L10-L11

Any chance we could break this cycle? Among other things, it would allow to include graphql-js seamlessly in ClojureScript via its new :npm-deps feature.

[IvanGoncharov]

The simplest solution would be to just merge wrappers.js into definitions.js.
Or we can minimize changes somehow?

@Jannis Do you want to work on this PR?

[Jannis]

@IvanGoncharov Sure, I can cook something up.