Currently channel filter construction returns a `StatusOr<T>`, this change makes it return a `StatusOr<P<T>>` where P is `unique_ptr`, `OrphanablePtr`, `RefCountedPtr`, `DualRefCountedPtr`, etc (most of the code really doesn't need to know, so I'm choosing to leave the flexibility).
That smart pointer is then stored in the channel stack instance, and dereferenced when needed.
This means that channel filters no longer need to be movable (which is a nice simplification), and puts these level-1 filters on a similar memory management track as the level-2 filters we have planned.
(this change also converts client load reporting to v3 apis -- it's a bit accidentally picked up, but seems ok to pull through too)
Closes#36355
COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/36355 from ctiller:objectify-me 0eb054b748
PiperOrigin-RevId: 625390977
58b254dacf