[C++] Eliminate Array boxing in scalar string kernels

[HyukjinKwon]

Describe the enhancement requested

#13364 introduced todos as below:

arrow/cpp/src/arrow/compute/kernels/scalar_string_ascii.cc

Line 398 in 53752ad

// TODO(wesm): rewrite to not require boxing

arrow/cpp/src/arrow/compute/kernels/scalar_string_ascii.cc

Line 450 in 53752ad

// TODO(wesm): rewrite to not require boxing

arrow/cpp/src/arrow/compute/kernels/scalar_string_ascii.cc

Line 2887 in 53752ad

// TODO(wesm): rewrite to not use ArrayData

arrow/cpp/src/arrow/compute/kernels/scalar_string_ascii.cc

Line 2916 in 53752ad

// TODO(wesm): rewrite to not use ArrayData

arrow/cpp/src/arrow/compute/kernels/scalar_string_ascii.cc

Line 2952 in 53752ad

// TODO(wesm): rewrite to not use ArrayData

Component(s)

C++