C++: Tensor migration to archetypes

Breaking out from: https://github.com/rerun-io/rerun/issues/2792

- [x] Implement f16 support in C++
- [x] #3881
- [x] Extensions
- [x] Unit test (constructors, serialization)
- [x] Doc example (partially done)
    - [x] includes image
- [ ] ~Implement jpeg_quality~