called. When the variable is a global the compiler is allowed to instantiate it more
aggresively and it might happen before the types involved are complete.
When it is inside a function the compiler can't instantiate it until after the
functions are called.

Remove an unused member from the vtable.
Replace transfer_slot_fn with a generic function when relocation is available to reduce duplication.

PiperOrigin-RevId: 492227302
Change-Id: I07499f63b91c59c0ae42402683387c7b84a6f0ee