The data flow library conflates pointers and objects enough for the
`definitionByReference` predicate to be too strict in some cases. It was
too permissive in other cases that are now (or will be) handled better
by field flow.
See also the change note entry.
This brings the annotation style in sync with how we annotate new tests
these days. I also changed a few annotations to have different expected
outcome based on my understanding of the code.
