[llvm] [Offload][WIP] Move `/openmp/libomptarget` to `/offload` (PR #75125)

[Louis Dionne via llvm-commits]

ldionne wrote:

> Libomptarget has been written for many years by many people. I would like to understand, does GH allow you to transfer over the history of contributions for each file you are moving?

Git normally handles file renaming quite well, so I would assume you won't even notice this when doing e.g. `git blame`.

The bigger question I'd have is about creating a new top-level directory in the monorepo -- typically this has been done mainly for new projects (e.g. llvm-libc, mlir, etc) and I wonder if there's some sort of process to add a new one of those. I don't care strongly, just mentioning it.

https://github.com/llvm/llvm-project/pull/75125