GPU implementation of AFT survival objective and metric (#5714)

* Add interval accuracy

* De-virtualize AFT functions

* Lint

* Refactor AFT metric using GPU-CPU reducer

* Fix R build

* Fix build on Windows

* Fix copyright header

* Clang-tidy

* Fix crashing demo

* Fix typos in comment; explain GPU ID

* Remove unnecessary #include

* Add C++ test for interval accuracy

* Fix a bug in accuracy metric: use log pred

* Refactor AFT objective using GPU-CPU Transform

* Lint

* Fix lint

* Use Ninja to speed up build

* Use time, not /usr/bin/time

* Add cpu_build worker class, with concurrency = 1

* Use concurrency = 1 only for CUDA build

* concurrency = 1 for clang-tidy

* Address reviewer's feedback

* Update link to AFT paper

tests/ci_build/Dockerfile.cpu

@@ -7,7 +7,7 @@ SHELL ["/bin/bash", "-c"]   # Use Bash as shell
 # Install all basic requirements
 RUN \
     apt-get update && \
-    apt-get install -y tar unzip wget git build-essential doxygen graphviz llvm libasan2 libidn11 liblz4-dev && \
+    apt-get install -y tar unzip wget git build-essential doxygen graphviz llvm libasan2 libidn11 liblz4-dev ninja-build && \
     # CMake
     wget -nv -nc https://cmake.org/files/v3.13/cmake-3.13.0-Linux-x86_64.sh --no-check-certificate && \
     bash cmake-3.13.0-Linux-x86_64.sh --skip-license --prefix=/usr && \