[MJAVADOC-624] tagletArtifacts throws exception in case artifact is a Java 9+ module

**[Martin Schelldorfer](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=schelldorfer)** opened **[MJAVADOC-624](https://issues.apache.org/jira/browse/MJAVADOC-624?redirect=false)** and commented

Auto-detect the class names for taglet artifacts fails in case artifact is a Java 9+ module.

When using configuration parameter tagletArtifacts, taglet classes are auto-detected.

JavadocUtil.getTagletClassNames() is scanning all classes in jar file (artifact).

Java 9+ modules contain the class module-info.class in jar file.

When trying to load module-info.class, the exception "java.lang.NoClassDefFoundError: module-info is not a class because access_flag ACC_MODULE is set" is thrown.

Class module-info has to be skipped in scanning loop.

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**Affects:** 3.1.1

**Remote Links:**
- [GitHub Pull Request #31
](https://github.com/apache/maven-javadoc-plugin/pull/31)

Start at JavadocUtil.getTagletClassNames(), which scans classes in each taglet artifact, and reproduce the failure with a Java 9+ module containing module-info.class. Check the scanning loop and confirm the completed behavior no longer attempts to load module-info.class or throws the reported NoClassDefFoundError.

Written by the indexing model from the issue text.