LightGBM

[R-package] Use Rprintf for logging in the R package (fixes #1440, fixes #1909) (#2901)

* [R-package] started cutting over from custom R-to-C interface to R.h

* replaced LGBM_SE with SEXP

* fixed error about ocnflicting definitions of length

* got linking working

* more stuff

* eliminated R CMD CHECK note about printing

* switched from hard-coded include dir to the one from FindLibR.cmake

* cleaned up formatting in FindLibR.cmake

* commented-out everything in CI that does not touch R

* more changes

* trying to get better logs

* tried ignoring

* added error message to confirm a suspicion

* still trying to find R during R CMD CHECK

* restore full CI

* fixed comment

* Update R-package/src/cmake/modules/FindLibR.cmake

* changed strategy for finding LIBR_HOME on Windows

* Removed 32-bit Windows stuff in FindLibR.cmake

* Update R-package/src/cmake/modules/FindLibR.cmake

* Update CMakeLists.txt

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

* Update CMakeLists.txt

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

* Update R-package/src/cmake/modules/FindLibR.cmake

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

* removed some duplication in cmake scripts

* Update R-package/src/cmake/modules/FindLibR.cmake

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

* Update R-package/src/cmake/modules/FindLibR.cmake

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

* Update R-package/src/cmake/modules/FindLibR.cmake

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

* Update R-package/src/cmake/modules/FindLibR.cmake

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

* Update R-package/src/cmake/modules/FindLibR.cmake

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

* Update R-package/src/cmake/modules/FindLibR.cmake

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

* added LIBR_CORE_LIBRARY back

* small fixes to CMakeLists

* simplified FindLibR.cmake

* some fixes for windows

* Apply suggestions from code review

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

* allowed for directly passing LIBR_EXECUTABLE to FindLibR.cmake

* reorganized FindLibR.cmake to catch more cases

* clean up inconsistencies  in R calls in FindLibR.cmake

* Update R-package/src/cmake/modules/FindLibR.cmake

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

* removed unnecessary log messages

* removed unnecessary unset() call

Co-authored-by: Nikita Titov <nekit94-08@mail.ru>