This patch introduces the concept of a Cached Resource that can be
cached across compositor evaluations as well as used by multiple
operations in the same evaluation. Additionally, this patch implements a
new structure for the realtime compositor, the Static Cache Manager,
that manages all the cached resources and deletes them when they are no
longer needed.
This improves responsiveness while adjusting compositor node trees and
also conserves memory usage.
Differential Revision: https://developer.blender.org/D16357
Reviewed By: Clement Foucault
