LightGBM

Pr3 monotone constraints splits penalization (#2939)

* Add the monotone penalty parameter to the config.

* Pass tree in the necessary functions so it can be used in ComputeBestSplitForFeature.

* Add monotone penalty.

* Added link to the original report.

* Add tests.

* Fix GPU.

* Revert "Pass tree in the necessary functions so it can be used in ComputeBestSplitForFeature."

This reverts commit 37757e8e8f3a2c82a604f4af9a926da616660d2e.

* Revert "Fix GPU."

This reverts commit e49eeee41c883f3c97fd5cdbd53c9288094bffb6.

* Added a shared pointer to the tree so the constraints can use it too.

* Moved check on monotone penalty to config.cpp.

* Python linting.

* Use AssertTrue instead of assert_.

* Fix penalization in test.

* Make GPU deterministic in tests.

* Rename tree to tree_ in monotone constraints.

* Replaced epsilon by kEplison.

* Typo.

* Make tree pointer const.

* Update src/treelearner/monotone_constraints.hpp

Co-Authored-By: Guolin Ke <guolin.ke@outlook.com>

* Update src/treelearner/monotone_constraints.hpp

Co-Authored-By: Guolin Ke <guolin.ke@outlook.com>

* Added alias for the penalty.

* Remove useless comment.

* Save CI time.

* Refactor test_monotone_penalty_max.

* Update include/LightGBM/config.h

Co-Authored-By: Nikita Titov <nekit94-08@mail.ru>

* Fix doc to be in line with previous config change commit.

Co-authored-by: Charles Auguste <auguste@dubquantdev801.ire.susq.com>
Co-authored-by: Guolin Ke <guolin.ke@outlook.com>
Co-authored-by: Nikita Titov <nekit94-08@mail.ru>