$JAVA10_HOME/bin/jmod describe $JAVA10_HOME/jmods/java.xml.bind.jmod > java.xml.bind.desc
And here is what I have got: java.xml.bind.desc
Specifically of interest is:
requires java.activation transitive
Therefore, dependency is explicit and transitive on Java 10 as well. It seems like it might be added automatically by --add-modules java.xml.bind, otherwise, the modular JVM shouldn't start with missing dependency error, as far as I understand.
Hence, it looks like this task might be a matter of prudence, not a strict requirement.