[llvm] [libsycl] Initial prefetch implementation for queue (PR #212104)

[via llvm-commits]

Robertkq wrote:

@KseniyaTikhomirova @sergey-semenov 

I've updated `queue_impl.cpp` to unconditionally use OL_MEM_MIGRATION_FLAG_HOST_TO_DEVICE and updated the unit tests accordingly. Also addressed the other comments on the PR.

Can you guys take another look over the PR when you have time and to approve workflows to see if tests pass also on PR? Locally, everything is fine

https://github.com/llvm/llvm-project/pull/212104