This changes varobj_iter::next to return a unique_ptr. This fits in
with the ongoing theme of trying to express these ownership transfers
via the type system.
gdb/ChangeLog
2020-12-11 Tom Tromey <tom@tromey.com>
* varobj.c (update_dynamic_varobj_children): Update.
* varobj-iter.h (struct varobj_iter) <next>: Change return type.
* python/py-varobj.c (struct py_varobj_iter) <next>: Change return
type.
(py_varobj_iter::next): Likewise.