[llvm] [LV] Run simplifyRecipes after addExplicitVectorLength (PR #200794)

[Mel Chen via llvm-commits]

Mel-Chen wrote:

I've ultimately decided to place the following two rules required by #199510 directly in optimizeMaskToEVLs for now:
```
vector.reverse(splice.left(poison, v, evl))
-->
vp.reverse(v, true, evl)

splice.right(vector.reverse(v), poison, evl)
-->
vp.reverse(v, true, evl)
```
The main reason is that both transformations convert non-VP intrinsics into VP intrinsics. If these rules were applied on non-EVL paths, I'm concerned they might introduce VP intrinsics there.

We can decide on the remaining permutation-elimination rules (for vector.reverse and splice) later.

https://github.com/llvm/llvm-project/pull/200794