[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.

LGTM.

I see there's a note in the spec: `async_work_group_copy and async_work_group_strided_copy for 3-component vector types behave as async_work_group_copy and async_work_group_strided_copy respectively for 4-component vector types. `. I'm not sure what that really means for our implementation which does a loop and a store.

I also wonder why we have `async/gentype.inc`. With this change, couldn't we just use `float/gentype.inc` and `integer/gentype.inc` in succession?

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