Remove static modifier on entityTypeToClass

Currently the NuxeoConverterFactory owns the static field entityTypeToClass used to determine java type from entity-type field present in JSON response.

This field is static because we need it in EntityValueDeserializer to determine type of fetched/resolved properties and type of context properties.

We want to avoid the static modifier by leveraging Jackson's attributes feature.

We will need to give this Map to Jackson like this:

ObjectReader objectReader = objectMapper.readerFor(javaType);
return objectReader.withAttribute("entityTypeToClass", entityTypeToClass).readValue(reader);

And then get it in deserializer like this:

public Object deserialize(JsonParser jp, DeserializationContext ctx) throws IOException {
  Map<String, Class<?>> entityTypeToClass = (Map<String, Class<?>>) ctx.getAttribute("entityTypeToClass");
  ...
}