Java: AnnotationElement does not extend Method

`AnnotationElement` is in CodeQL effectively a `Method` (i.e. `forall(AnnotationElement e | e instanceof Method)` will always hold), however it does not extend Method.

This makes usage confusing because Java interfaces and classes can have (despite it being discouraged) an `AnnotationType` as supertype. So it is not obvious how CodeQL will handle this unless you look in the source and find out how `AnnotationElement` is defined.

Slightly related to #3708