[llvm] [OFFLOAD][OMP] Move OpenMP kernel argument processing from plugins (PR #213867)

[Kevin Sala Penades via llvm-commits]

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kevinsala wrote:

I think we can merge the field(s) from `KernelExtraArgsTy` to `KernelLaunchArgsTy` and remove `KernelExtraArgsTy`. I can do it in a separate PR.

https://github.com/llvm/llvm-project/pull/213867