No way to access custom metadata

[jdidion]

CWL provides the ability to use custom metadata via $namespaces. However, the objects generated by the Java parser do not contain the metadata, or at least there's no method by which to access it.

[jdidion]

The same is true for $schemas

[mr-c]

$namespaces are stored in the private loadingOptions_ class member in each cwljava object; can you access that from Scala or do we need to add a public accessor function?

https://github.com/common-workflow-lab/cwljava/blob/13ee0b762465307f4103abad15e1a3b31da73656/src/main/java/org/w3id/cwl/cwl1_2/utils/Loader.java#L29

https://github.com/common-workflow-lab/cwljava/blob/13ee0b762465307f4103abad15e1a3b31da73656/src/main/java/org/w3id/cwl/cwl1_2/WorkflowImpl.java#L79

While there is a schemas class member for LoadingOptions it doesn't appear to be used. This would be fixable, if you'd like.