The vector pass and potentially other vectors that store 4 values are
stored wrongly, in particular, the last channel is ignored. To fix this
we identify if a vector pass is 4D and store the information in the
result meta data, then use this information to either save a 3D or a 4D
pass in the File Output node.
This is a CPU implementation of the same mechanism in the GPU compositor
implemented in 57a6832b17. The CPU implementation is a bit more complex
because the CPU compositors stores 4D vectors in color images internally
which can lead to information loss in case of implicit conversion when
the File Output has vector sockets. So what we do is force all vector
inputs to the File Output operation to be color, then save that as 3D or
4D depending on the meta data as well as the original UI socket type.
Pull Request: https://projects.blender.org/blender/blender/pulls/124580
308b53746b