JSON tree algorithm code reorg (#16836)

This PR moves JSON host tree algorithms to separate file.
This code movement will help #16545 review easier.

The code is moved to new file and reorganized for code reuse.
Very long function `make_device_json_column` is split into
- code block with `reduce_to_column_tree` call
- code moved to function `build_tree`
- code moved to function `scatter_offsets`

No new functionality is added in this PR.

Authors:
  - Karthikeyan (https://github.com/karthikeyann)

Approvers:
  - Kyle Edwards (https://github.com/KyleFromNVIDIA)
  - Shruti Shivakumar (https://github.com/shrshi)
  - MithunR (https://github.com/mythrocks)

URL: #16836

cpp/CMakeLists.txt

@@ -378,6 +378,7 @@ add_library(
   src/io/csv/reader_impl.cu
   src/io/csv/writer_impl.cu
   src/io/functions.cpp
+  src/io/json/host_tree_algorithms.cu
   src/io/json/json_column.cu
   src/io/json/json_normalization.cu
   src/io/json/json_tree.cu