GraphQLErrorExtensions' classification property had a type of String, but in practice an ErrorClassification may be mapped to any JSON serializable type; this is actually the case in practice when using libraries such as graphql-java-extended-validation, which may return a Map for its ErrorClassification. Switch the type to Any, so that such responses can be deserialized, and add a simple test case.
GraphQLErrorExtensions' classification property had a type of String, but in practice an ErrorClassification may be mapped to any JSON serializable type; this is actually the case in practice when using libraries such as graphql-java-extended-validation, which may return a Map for its ErrorClassification. Switch the type to Any, so that such responses can be deserialized, and add a simple test case.
Fixes #1146