Add support for shader output property in ndrArnold parser

[frenchdog]

Describe the feature you'd like Ability to get information about an Arnold node output when querying an SdrShaderNode.

Describe the solution you'd like Since an Arnold node output does not have an explicit name, calling NdrNode::GetOutputNames() would return a vector with only one "out" string. Calling SdrShaderNode::GetShaderOutput("out") would return a valid SdrShaderProperty. Such property would give information like its type and if it is an array.

Additional context Such feature would allow to write generic code for applications using the NdrDiscoveryPlugin mechanism to create shader nodes.