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
File output node always received the resolution from the first socket.
When that socket didn't had a link it would use a resolution of 0,0.
What lead to not saving the file at all.
This only effected Multi layer OpenEXR files.
This change would go over all the links to find the first valid
resolution.
