[flang] [llvm] [flang] Implement SPLIT intrinsic subroutine with tests (PR #185584)

[Tarun Prabhu via llvm-commits]

https://github.com/tarunprabhu commented:

 I am not the best person to review this since I am not very familiar with the runtime code, nor the F2023 standard. I have some comments, but it would be better if someone more familiar with this part of the compiler and standard would take a closer look.

https://github.com/llvm/llvm-project/pull/185584