Enhance the Gradle build as necessary after removing Ant support

Once the bulk of the Ant build system is removed, stuff will come bubbling up out of the cracks, especially as we try the first 9.0 release which will be Gradle only. Here we list some of the areas we'll have to be aware of. Please add as you see fit. Assigning to myself to track, but I certainly don't want hog all the fun.

• Remove Maven support and replace with "The Gradle Way" of doing Maven. See LUCENE-9077 (Dawid)

• • Remove all of dev-tools/maven?
  • Other dev-tools files no longer used, check if any Gradle build file references and remove if not.
• Move Jenkins over to use Gradle only
• Verify reference guide build works under Gradle
• Smoke tester
• Remove anything having to to with Clover (obsolete as of Java 11)
• Remove all of lucene/tools (Ivy, forbiddenapis,...}}
• Remove obsolete files in root dirs of lucene and solr (like ivy-versions.props, now integrated into gradle)
• Remove Maven build files (obsolete with Gradle)
• Hoss's test rollups?
• Enable javadocs after ant stops being used (LUCENE-9441)
• fix some relative links in javadocs which contain ant module names
• dev-tools/scripts/* There are a lot of mentions of ant in the .py files, and some in the README.md. This one should probably be its own JIRA since it'll require quite a bit of verification...
• Make "the best damn beasting script in the world" work with the Gradle build. (see LUCENE-9465, LUCENE-9472 for alternatives)
• Update the release documentation to reflect Gradle (LUCENE-9488)
• Clean up anything in lucene/tools
• Clean up Confluence, in particular any page that mentions IDEs. The "How to Contribute" page has several links to various bits and pieces of how to use IDEs, and some mention ant.