This patch allows point and spline attributes to be transferred to the
mesh generated by the curve to mesh node. All dynamic named and
anonymous attributes are transferred. So a user-created attribute will
be transferred, but "radius", "tilt" or the handle position attributes
won't be transferred by default and will need to be copied first.
This trade-off is made for performance, since most of the time, users
won't need these attributes copied.
Generally, attributes are transferred to the point/vertex domain.
However, if they have the same name as a built-in mesh attribute that
only exists on a different domain, like "shade_smooth", then they can
be transferred directly to that domain as well. Conversion directly to
the face corner domain is not necessary because there are no builtin
face corner attributes. I see this conversion directly to other domains
as an optimization we could use behind the scenes in the future as well,
when named attributes are less common.
For performance, I haven't tested which of the following is better:
```
for each spline combination:
for each attribute:
for each attribute:
for each spline combination:
```
For now I used the existing loop to avoid more threading overhead.
Differential Revision: https://developer.blender.org/D12363