This is a code refactor in preparation of supporting canvas
compositing. See {D12466}.
No functional changes, all canvases are at (0,0) position matching
tiled implementation.
Differential Revision: https://developer.blender.org/D12465
Adds full frame implementation to "Composite", "File Output" and
"Split Viewer" nodes.
The other nodes in "Output" submenu are implemented separately.
No functional changes.
Reviewed By: jbakker
Differential Revision: https://developer.blender.org/D12091
