This patch adds support for accessing corner attributes on the point domain.
The immediate benefit of this is that now (interpolated) uv coordinates are
available on points without having to use the Point Distribute node.
This is also very useful for parts of T84297, because once we have vertex
colors, those will also be available on points, even though they are stored
per corner.
Differential Revision: https://developer.blender.org/D10305
