Fill in default values for missing arguments on applied directives #821

When an applied directive leaves out an argument that has a default value, SchemaParser builds the GraphQLAppliedDirective without that argument. graphql-java's own SchemaGenerator adds the missing arguments with their defaults (SchemaGeneratorAppliedDirectiveHelper.transferMissingAppliedArguments), so the two produce different schemas from the same SDL.

directive @auth(role: String = "USER") on FIELD_DEFINITION

type Query {
    secret: String @auth
}

schema.queryType.getFieldDefinition("secret")
    .getAppliedDirective("auth")
    .getArgument("role")
// SchemaGenerator: "USER"
// graphql-java-tools: null

#818 works around this for @deprecated only, because a bare @deprecated with no reason makes SchemaPrinter throw a NPE. The general fix is to do the same for every directive in SchemaParser.buildAppliedDirectives: for each argument of the directive definition that isn't in the applied directive but has a default, add it with the default value. The @deprecated special case can then be removed.

This changes behaviour: code that expects getArgument(...) to be null for an omitted argument will now get the default value, so it should go in a minor release with a note in the release notes.