[llvm] [NFC][LV]: Differentiate between Pred and Unpred masked operations. (PR #169509)

[Hassnaa Hamdi via llvm-commits]

hassnaaHamdi wrote:

@fhahn 
For the proposed solution of having 2 instances of `VectorizationCostModel`, one of them is for unpredicated vectorized loop, so it will use the `UnpredMaskedOp` to store/check the conditional/masked operations, the other cost model instance will be for the predicated vectorized epilogue which will use the `PredMaskedOp`. Both instances of cost model will use single instance of `LoopVectorizationLegality`, that’s why we need to have both lists.

https://github.com/llvm/llvm-project/pull/169509