Get CUDA code to compile with clang CUDA and without CUDA opencv#3800

Changelist:
- there are some syntactic changes: `<< <` -> `<<<`. For some reason, I do not need to change all those in the code.
-  `::min` -> `std::min` in `__host__` code
- `modules/cudaimgproc/src/moments.cpp` needs to have the CUDA code in the `#ifdef`
- The signature of `cv::cuda::swapChannels` is not exactly the same as the C++ one in `modules/cudaimgproc/src/color.cpp` 
- `cv::cuda::FarnebackOpticalFlow::create` needs to be explicit about which FarnebackOpticalFlow it returns

### Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch

…op_with_scalar

`cudaarithm`: fix python bindings for binary ops involving scalars