Export complexity directive

[dimatill]

In such a way complexity directive can be reused in code first approach to include directive definition in generated typeDefs:

new GraphQLSchema({
  directives: [complexityDirective()]
})

[ivome]

Thanks for the PR!

I added a few suggestions. Could you add some tests and docs for the changes?

[ivome]

Let's create a type for this that we can then also export ComplexityDirectiveOptions and reuse externally.

[ivome]

Suggested change

	export function complexityDirective(name: string = 'complexity') {
	export function createComplexityDirective(options?: ComplexityDirectiveOptions = {}) {

This way it's clearer that the function is not the directive itself but rather a creator, and passing the entire options object keeps the interface stable in case we decide to extend it later.

[dimatill]

@ivome I've pushed suggested changes.
Had to use a workaround inside tests by rebuilding the code first schema from typeDefs because of graphql-js <= 14 prints descriptions in different ways (printSchema(schema) vs print(astNode)) and directive from code first schema has no astNode. left this comment inside tests. Let me know if you have any idea how to write tests in another way

[ivome]

Thanks for adding those changes, looks good now. I'm fine with the workaround for graphql-js <= 14 since it's just in the tests. Once we drop support for the older version, we can remove this, but 14 is still pretty widely used.