[llvm] [DAGCombiner] Expose CSE for shifts of logic operations (PR #213091)

[Justin Fargnoli via llvm-commits]

justinfargnoli wrote:

In the description `SX = shl X, S` should align with the declarations below. e.g.

```
                               SX = shl X, S
  P1 = shl (LOP X, C1), S  ->  P1 = LOP SX, (C1 << S) ; constants will be folded
  P2 = shl (LOP X, C2), S      P2 = LOP SX, (C2 << S) ; constants will be folded
  P3 = shl (LOP X, C3), S      P3 = LOP SX, (C3 << S) ; constants will be folded
```

https://github.com/llvm/llvm-project/pull/213091