[llvm] [SLP] Add store-to-load forwarding conflict cost for widened store chains (PR #199606)

[Milin Bhade via llvm-commits]

mbhade-amd wrote:

> 1.Rebase 2. Did you use AI tool? Add to to the commit message 3. Add compile-time/runtime data

Rebased. I have added AI usage, in PR description.

https://github.com/llvm/llvm-project/pull/199606