feature request: `--print-avro` should resolve `extends` references

Hi! Benten relies on the schema to create all the data structures needed to analyze CWL documents. I use the schema in `.json` format as generated by `--print-avro`. Any references mentioned in any `extends` field in a definition I can incorporate if they are to be found in that `.json` file somewhere. However I see that some references are not, such as `RecordSchema`, `InputSchema` and so on. It would be nice if `--print-avro` resolved all `extends` references or at least placed them in the output `.json`. Thanks!