We use the `final` argument in object iteration to denote
`OC_F_PRIVATE | OC_F_HFM | OC_F_HFP`.

As we now have `VDP_END` to mark the final bit of data, so should the
iterator flag be named `_END`. This also parallels `VDP_FLUSH` vs.
`OBJ_ITER_FLUSH`.

Supported by martin

Ref #3298