[llvm] [SLP] Account for GEP pointer-chain cost when root scalars feed load/store indices (PR #192726)

[Alexey Bataev via llvm-commits]

alexey-bataev wrote:

> On line 4749, there's a typo in the comment which could get wrapped in with this MR: (`reaplced` -> `replaced`)
> 
> ```
>   /// A list of GEPs which can be reaplced by scalar GEPs instead of
>   /// extractelement instructions.
>   SmallPtrSet<Value *, 4> ExternalUsesAsOriginalScalar;
> ```

Not related to the PR, must be fixed in a separate patch

https://github.com/llvm/llvm-project/pull/192726