Way to map directly to/from JsonGenerator and JsonParser

Some data binding frameworks provide a way to do mappings to/from parsers and generator.

JAXB:

https://docs.oracle.com/javase/8/docs/api/javax/xml/bind/JAXB.html#unmarshal-javax.xml.transform.Source-java.lang.Class-
https://docs.oracle.com/javase/8/docs/api/javax/xml/bind/JAXB.html#marshal-java.lang.Object-javax.xml.transform.Result-

(see StAXResult and StAXSource)

Jackson:

https://fasterxml.github.io/jackson-databind/javadoc/2.7/com/fasterxml/jackson/databind/ObjectMapper.html#writeValue(com.fasterxml.jackson.core.JsonGenerator,%20java.lang.Object)
https://fasterxml.github.io/jackson-databind/javadoc/2.7/com/fasterxml/jackson/databind/ObjectMapper.html#readValues(com.fasterxml.jackson.core.JsonParser,%20java.lang.Class)

This is a useful feature as it allows a user to leverage the mapping rules without requiring a serialization format (JSON text or some other format). Also some implementations might only implement parser/generator and not implement JsonProvider.

Could we add to/from JSON methods for JsonParser and JsonGenerator?

See also: https://github.com/eclipse-ee4j/yasson/issues/245

No repository files or tests are named. Start by reviewing the JSON-B API definitions for JsonParser and JsonGenerator, then compare the linked Jackson ObjectMapper methods and JAXB examples; done means an agreed design for mapping to and from these parser/generator types.

Written by the indexing model from the issue text.