Rewrite Annotation processor used to validate components.txt into a Checkstyle check

Right now we use an annotation processor (see XCOMMONS-692). However this is causing problems:

• Issue with IDEs, especially IntelliJ IDEA: https://youtrack.jetbrains.com/issue/IDEA-133120
• Annotation processors shouldn't depend on non-java inputs (components.txt here), see comments at https://issues.apache.org/jira/browse/MCOMPILER-122?focusedCommentId=14429056&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14429056
• There are warnings generated in the build, for example "warning: [processing] No processor claimed any of these annotations:..."