[#6105] JDK8 javadoc issues

Fixes a bunch of javadoc the JDK8 linter doesn't like. All changes are stylistic only and shouldn't affect the content.

The linter is ignored on both the module with XJC generated classes as I don't think it is possible to make xjc use &gt; rather than > when generating javadoc, and the TCK module as there are a bunch of invalid tags that look like they are used by some other tooling not included in this repo.