JSON spark reader plan for 24.12

[karthikeyann]

These are the planned optimizations and bug fixes for JSON spark reader for 24.12 release.

• Memory optimization PR JSON tokenizer memory optimizations #16978

• Runtime mitigation issue - Multi-stage FST implementation (Elias, Shruti) [FEA] Faster path for calculating total output symbols in FST #17114

• input schema issue/PR (New Feature)

  • [FEA] read_json should output all-nulls columns for the schema columns that do not exist in the input #17091,
  • [FEA] The output columns of read_json need to follow depth-first-search order as in the input schema #17090,
  • [FEA] Implement a better JNI function to assemble the output columns from cudf::read_json #17002,
  • [BUG] cudf::io::read_json does not verify output column structures with the input schema #16799,
  • [BUG] Requested types ignored if prune_schema is enabled for JSON reading #16797
  • PR Add optional column_order in JSON reader #17029

• Performance: Preprocessing: nullify empty lines PR add option to nullify empty lines #17028

• Bugfix: last invalid json is not error - [BUG] cudf::read_json incorrectly parses invalid JSON string #16999

• Bugfix: disable array of arrays for spark - disable array of arrays for recovery with null #17030

• Performance: mega kernel - [FEA] Implement merged 'mega' kernel to parse leaf-level columns in JSON reader #16965

• [FEA] Improve GpuJsonToStructs performance NVIDIA/spark-rapids#11560 (input schema, and post-processing move columns without copying)

  • Convert strings columns output from cudf::read_json to other types NVIDIA/spark-rapids-jni#2510