[clang] [flang] [flang][driver] Rename `flang-new` as `flang` (PR #74377)

[Kiran Chandramohan via cfe-commits]

kiranchandramohan wrote:

I am assuming you have got a go-ahead from the code owner and others involved in the discourse discussion. It is probably good to post a link to this patch in the relevant discourse post for information and confirmation.

https://github.com/llvm/llvm-project/pull/74377