[llvm] [Delinearization] Add function for fixed size array without relying on GEP (PR #145050)

[Ryotaro Kasuga via llvm-commits]

kasuga-fj wrote:

If you're referring to [my previous comment](https://github.com/llvm/llvm-project/pull/145050#discussion_r2172061181), I meant "this part of the code" as in "the code from lines 774 to 777". Sorry for confusion, but I didn't mean to imply that the entire change in this PR is just for testing purposes. Once this is merged, I'm considering submitting another patch to replace the call to `tryDelinearizeFixedSizeImpl` in DA with the new function.

https://github.com/llvm/llvm-project/pull/145050