[JENKINS-20739] Filter descriptors before adding them to hetero-list

This allows implementations of `DescriptorVisibilityFilter` to hide items
with descriptors from users to prevent them from being added via the UI
using `hetero-list`.

This is already implemented in `/lib/hudson/newFromList/form.jelly`, as well as `Functions.getSortedDescriptorsForGlobalConfig(Predicate)`, but nowhere else.