[SSADestroyHoisting] Fixed pointer handling.
Previously, SSADestroyHoisting was attempting to check whether an
unknown use of a variable was an address_to_pointer.
UniqueStorageUseVisitor, however, doesn't call back with that
instruction. Instead, it adds its uses to the stack of uses to visit.
Instead, we need to check whether the use was produced by an
address_to_pointer or more generally whether it's a
BuiltinRawPointerType.
