[libclc] [libclc] Add v3 variants of async_work_group_copy/async_work_group_strided_copy/prefetch (PR #137932)

[Fraser Cormack via cfe-commits]

https://github.com/frasercrmck approved this pull request.

Thanks. We could probably come up with some kind of combined `gentype.inc` that does them both at once (though both currently `undef` `__CLC_BODY` after they finish so we'd need to be able to stop that, or preserve `__CLC_BODY` across gentypes).

Come to think of it, we do a lot of unnecessary `undef __CLC_BODY` around the codebase. I will try to clean that up in a separate PR.

https://github.com/llvm/llvm-project/pull/137932