Add FQCNs from classes and interfaces in a Java artifact

[bhermann]

Is your feature request related to a problem? Please describe.
In some use cases (e.g., API matching) we would like to identify artifacts in the index by a FQCN (fully-qualified class name) contained in the artifact.

Describe the solution you'd like
Take a JAR file and use OPAL to extract the names of all classes and interfaces contained.

Describe alternatives you've considered
None considered, but other bytecode engineering frameworks might be faster.

Additional context
none