[llvm] [Offload] Implement the remaining initial Offload API (PR #122106)

[Joseph Huber via llvm-commits]

================
@@ -16,8 +16,8 @@ def : Function {
     let details = [];
     let params = [
         Param<"ol_queue_handle_t", "Queue", "handle of the queue", PARAM_IN>,
----------------
jhuber6 wrote:

This is also similar to stuff like CUDA's `cuLaunchHostFunc` which is also a handy way to register callbacks on kernel completion, so I think it's something we should expose.

https://github.com/llvm/llvm-project/pull/122106