Rework logic in cudf::strings::split_record to improve performance (#…

…12729)

Updates the `cudf::strings::split_record` logic to match the more optimized code in `cudf::strings:split`.
The optimized code performs much better for longer strings (>64 bytes) by parallelizing over the character bytes to find delimiters before determining split tokens. 
This led to refactoring the code so it both APIs can share the optimized code.
Also fixes a bug found when using overlapped delimiters.
Additional tests were added for multi-byte delimiters which can overlap and span multiple adjacent strings.

Closes #12694

Authors:
  - David Wendt (https://github.com/davidwendt)

Approvers:
  - Nghia Truong (https://github.com/ttnghia)
  - Yunsong Wang (https://github.com/PointKernel)
  - https://github.com/nvdbaranec

URL: #12729

cpp/benchmarks/string/split.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021-2022, NVIDIA CORPORATION.
+ * Copyright (c) 2021-2023, NVIDIA CORPORATION.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -57,12 +57,12 @@ static void BM_split(benchmark::State& state, split_type rt)
 
 static void generate_bench_args(benchmark::internal::Benchmark* b)
 {
-  int const min_rows   = 1 << 12;
-  int const max_rows   = 1 << 24;
-  int const row_mult   = 8;
-  int const min_rowlen = 1 << 5;
-  int const max_rowlen = 1 << 13;
-  int const len_mult   = 4;
+  int constexpr min_rows   = 1 << 12;
+  int constexpr max_rows   = 1 << 24;
+  int constexpr row_mult   = 8;
+  int constexpr min_rowlen = 1 << 5;
+  int constexpr max_rowlen = 1 << 13;
+  int constexpr len_mult   = 2;
   for (int row_count = min_rows; row_count <= max_rows; row_count *= row_mult) {
     for (int rowlen = min_rowlen; rowlen <= max_rowlen; rowlen *= len_mult) {
       // avoid generating combinations that exceed the cudf column limit