Split Transform3D component union type into components

Remaining todo items:

[x] introduce LeafTransform3D with all the associated ripple effect [...] https://github.com/rerun-io/rerun/pull/7015
[x] finish removal of legacy types (or deprecate where appropriate) https://github.com/rerun-io/rerun/pull/7000
[x] deprecate (or remove for new stuff) stray rotation components from archetypes and add out of tree support there https://github.com/rerun-io/rerun/pull/7029
- [x] box3d
- [x] ellipsoids (remove!)
- [ ] what else?
[x] remove old Rotation3D component https://github.com/rerun-io/rerun/pull/7030
[x] use LeafTransform3D on Box3D & Arrows3D & Ellipsoids instead (don't forget to point out transform relationship!) https://github.com/rerun-io/rerun/pull/7029
[ ] extra pass over migration guide - is all correct, is something missing

// Two possibilities:
// - Only legal to set one of them
// - Or apply them all in deterministic order
archetype Transform {
    mat4: Option<Mat4>,
    translation: Option<Translation3>,
    mat3: Option<Mat3>,
    rotation: Option<Rotation3D>,
    scale3: Option<Scale3D>,
    scale: Option<Scale>,
}

Old proposal

How to handle OutOfTreeTransform:

Introduce a new boolean component that coerces a transform batch to be out of tree. OutOfTreeTransform { enabled: bool } if one encounters several several parent transforms and if they have the OutOfTreeTransform == false the viewer issues a warning and resolves in a best effort manner

To consider: The fallback provider for OutOfTreeTransform can be clever and look at transform counts, automatically assuming true if there's several transforms.

Drawback: Can no longer have out of tree transform side by side with in-tree transforms

rerun-io / rerun

Split Transform3D component union type into components #6831

Old proposal