Blender Git Loki

Fix T87194: custom attributes not accessible with Cycles Volume

Custom properties defined on objects are not accessible from the
attribute node when rendering a volume in Cycles. This is because
this case is not handled.

To handle it, added a primitive type for volumes in the kernel,
which is then used in the initialization of ShaderData and to
check whether an attribute lookup is for a volume.

`volume_attribute_float4` is also now checking the attribute
element type to dispatch to the right lookup function.

Reviewed By: #cycles, brecht

Maniphest Tasks: T87194

Differential Revision: https://developer.blender.org/D11728