Replace old host tree algorithm with new algorithm in JSON reader (#1…

…7019)

This PR replaced old tree algorithm in JSON reader, with experimental algorithms and removed the experimental namespace.

Changes are old tree algorithm code removal,  experimental namespace removal, code of `scatter_offsets` moved, always call new tree algorithm.
No functional change is made in this PR. All unit tests should pass with this change.

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

Approvers:
  - Shruti Shivakumar (https://github.com/shrshi)
  - Vukasin Milovanovic (https://github.com/vuule)

URL: #17019