This PR backports CUDA implementation of YOLOv4x-mish new_coords by @erikguo.
Original PR: #19221, related: #18975

force_builders=Custom
build_image:Custom=ubuntu-cuda:18.04
test_modules:Custom=dnn,python2,python3,java

buildworker:Custom=linux-4
test_opencl:Custom=ON
test_bigdata:Custom=1
test_filter:Custom=*

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• I agree to contribute to the project under Apache 2 License.
• To the best of my knowledge, the proposed patch is not based on a code under GPL or other license that is incompatible with OpenCV
• The PR is proposed to proper branch
• There is reference to original bug report and related work
• There is accuracy test, performance test and test data in opencv_extra repository, if applicable
  Patch to opencv_extra has the same branch name.
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