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

[Brad Richardson via cfe-commits]

everythingfunctional wrote:

> > Not that it's the end of the world if this doesn't get in before the this release, but @sscalpone , exactly what feedback are we wanting before merging?
> 
> IIUC, this: https://discourse.llvm.org/t/proposal-rename-flang-new-to-flang/69462/55

ok, but is there some threshold of percent that pass, or a specific list that we want to be sure pass? My understanding is that we've been running (at least a subset of) the gfortran test suite for a while now. What makes the current results not sufficient?

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