Adds full frame implementation to Image node operations.
Mostly refactored into buffer utility methods for reuse in other
operations.
No functional changes.
1.8x faster than tiled fallback.
Reviewed By: jbakker
Differential Revision: https://developer.blender.org/D11559
These variables and methods should make it easier to loop through buffers elements/pixels. They take into account single element buffers.
Single element buffers can be used for set operations to reduce memory usage.
Usage example: P2078
Reviewed By: #compositing, jbakker
Differential Revision: https://developer.blender.org/D11015
