Adding some interface default method implementations (#2879)

* Adding some interface default method implementations rather than catching AbstractMethodError or providing partial implementation classes.

* Show Javadoc warnings and errors, but not ‘Generating …/core/target/site/apidocs/jenkins/model/lazy/class-use/AbstractLazyLoadRunMap.html...’ and the like.

* Javadoc fixes.

* Review comments from @oleg-nenashev.

* Test fixes.

* Remove the unused import