[MJAVADOC-744] Maven coordinates in Javadoc

**[Elliotte Rusty Harold](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=elharo)** opened **[MJAVADOC-744](https://issues.apache.org/jira/browse/MJAVADOC-744?redirect=false)** and commented

Add an option to the javadoc plugin to include the Maven coordinates (group:artifact:version) of a class in its Javadoc.

I noticed this morning for about the 173rd time that I could google for the API doc of a class I needed, but still couldn't figure out which artifact I needed to add to my pom.xml to include that class in my project.

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No further details from [MJAVADOC-744](https://issues.apache.org/jira/browse/MJAVADOC-744?redirect=false)

No source files or tests are named in the issue. Start by locating the Maven Javadoc Plugin's option handling and Javadoc generation entry points, then determine how group:artifact:version should be associated with each class. Done means a documented plugin option can include the Maven coordinates in generated Javadoc, with coverage for the resulting output.

Written by the indexing model from the issue text.