Add a quaternion rotation socket type, and using the recently added
rotation attribute type, support the type in most of the multi-type
geometry nodes, and modifier attribute inputs and outputs.
The socket is still exposed with an XYZ Euler default value.
In the future we can add modes to this rotation value similar
to object rotations.
Rotation values have no implicit conversions to other types.
Nodes to convert to and from rotation values will be added
in a follow-up commit.
For now, the new socket type is hidden behind and experimental
option, because we haven't chosen the final color for it yet.
Pull Request: https://projects.blender.org/blender/blender/pulls/108903
63dae2a105