[LifetimeAnalysis] Do not forbid void deref type in gsl::Pointer/gsl::Owner annotations

It turns out it is useful to be able to define the deref type as void.
In case we have a type erased owner, we want to express that the pointee
can be basically any type. It should not be unnatural to have a void
deref type as we already familiar with "pointers to void".

Differential Revision: https://reviews.llvm.org/D72097