NonDereferenceable denotes the intent that a pointer will (most likely) not be
dereferenced, but its numeric value may be used for e.g. logging purposes.
Dereferencing operations are explicitly disabled to avoid unintentional misuses.
Casting is still possible between related types (same as with raw pointers),
but pointers stay safely stored inside NonDereferenceable objects. These casts
do not trigger `clang++ -fsanitize=vptr` errors.
MozReview-Commit-ID: 5885pB7hSFR
--HG--
extra : rebase_source : 3c4011da64d84f1b19991742b76bafbffa90d590
