Fix add extension types

[mgagliardo91]

Description

Resolves graphile/graphile.github.io#368

This PR updates the makeExtendSchemaPlugin to add all new types to the schema during the GraphQLSchema hook so that they are available in the final schema, regardless of explicit usage. Up to this point, types were only added to the schema if they were explicitly (direct or recursively) mapped from a Query/Mutation.

Performance impact

Minimum - runs during the GraphQLSchema hook.

Security impact

N/A

Checklist

• My code matches the project's code style and yarn lint:fix passes.
• I've added tests for the new feature, and yarn test passes.
• I have detailed the new feature in the relevant documentation.
• I have added this feature to 'Pending' in the RELEASE_NOTES.md file (if one exists).
• If this is a breaking change I've explained why.

[benjie]

This is great and very simple, but the problem is that it significantly changes the generated schema order - putting the types added by makeExtendSchemaPlugin above everything else.

I think that graphql walks the types in order, so we may be able to solve this fairly simply by just ensuring that the Query, Mutation and Subscription types are processed first. That might look something like this:

Suggested change

	...(schema.types || []),
	...typeExtensions.GraphQLSchema.types,
	...newTypes,
	...([
	build.getTypeByName(inflection.builtin("Query")),
	build.getTypeByName(inflection.builtin("Mutation")),
	build.getTypeByName(inflection.builtin("Subscription")),
	].filter(_ => _)),
	...(schema.types || []),
	...typeExtensions.GraphQLSchema.types,
	...newTypes,