Blender Git Loki

Cycles X: Don't cache Pass info as a field

Avoiding such caching makes the Pass to fit generic nodes much
better: no need to worry about maintaining the information in
sync with the socket values.

The PassInfo construction is cheap, so the change should not
cause any time penalties.

No functional changes, just making Pass more re-usable outside
of Scene/Film for an upcoming development.

Differential Revision: https://developer.blender.org/D12431