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Previously #6086 added ROCm support but after numerous rebases it lost
critical changes. This PR restores the ROCm build.

There are many source file changes but most were automated using the
following:

```bash
for f in `grep -rl '#ifdef USE_CUDA'`
do
    sed -i 's@#ifdef USE_CUDA@#if defined(USE_CUDA) || defined(USE_ROCM)@g' $f
done

for f in `grep -rl '#endif  // USE_CUDA'`
do
    sed -i 's@#endif  // USE_CUDA@#endif  // USE_CUDA || USE_ROCM@g' $f
done
```

* [ci] speed up if-else, swig, and lint conda setup

* add 'source activate'

* python constraint

* start removing cuda v1

* comment out CI

* remove more references

* revert some unnecessaary changes

* revert a few more mistakes

* revert another change that ignored params

* sigh

* remove CUDATreeLearner

* fix tests, docs

* fix quoting in setup.py

* restore all CI

* Apply suggestions from code review
Co-authored-by: shiyu1994 <shiyu_k1994@qq.com>

* Apply suggestions from code review

* completely remove cuda_exp, update docs

---------
Co-authored-by: shiyu1994 <shiyu_k1994@qq.com>

[CUDA] Add Poisson regression objective for cuda_exp and refactor objective functions for cuda_exp (#5486)

* add poisson regression objective for cuda_exp

* enable Poisson regression for cuda_exp

* refactor cuda objective functions

* remove useless changes

* fix linter errors

* remove redundant buffer in cuda poisson regression objective

* fix log of cuda_exp binary objective

* fix threshold of poisson objective result

* remove useless changes

* fix compilation errors

* add cuda quantile regression objective

* remove cuda quantile regression objective
Co-authored-by: James Lamb <jaylamb20@gmail.com>

* add lambdarank for cuda_exp

* support unlimited number of ranks in labels

* fix lint errors

* remove warning for lambdarank with cuda_exp

* Update src/objective/cuda/cuda_rank_objective.hpp
Co-authored-by: Nikita Titov <nekit94-08@mail.ru>

* Update src/objective/cuda/cuda_rank_objective.hpp
Co-authored-by: Nikita Titov <nekit94-08@mail.ru>
Co-authored-by: Nikita Titov <nekit94-08@mail.ru>