Compositor: Export operation results as debug option

When fixing issues, seeing operation results can be helpful for
detecting which operation went wrong.

This commit adds an option for exporting all operations results to
image files.
Exceptions are:
- Output operations: They are already exported or can be seen in UI.
- Constant operations: There are too many and is rarely useful.

They are exported to "<temp session folder>/COM_operations/"
with filenames "<operation class name>_<operation id>.png".
Only works on full frame execution mode.

Reviewed By: jbakker

Differential Revision: https://developer.blender.org/D11722

source/blender/compositor/intern/COM_FullFrameExecutionModel.cc

@@ -104,6 +104,7 @@ void FullFrameExecutionModel::render_operation(NodeOperation *op)
   op->render(op_buf, areas, input_bufs);
   active_buffers_.set_rendered_buffer(op, std::unique_ptr<MemoryBuffer>(op_buf));
 
+  DebugInfo::operation_rendered(op, op_buf);
   operation_finished(op);
 }