[clang] [flang] [llvm] [flang][driver] rename flang-new to flang (PR #110023)

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h-vetinari wrote:

If you want to compare notes, I recently rebased #74377, and tried to pick up all additional occurrences I could find. Here's the [branch](https://github.com/h-vetinari/llvm-project/tree/flang_rename).

https://github.com/llvm/llvm-project/pull/110023