[llvm] [LV][VPlan] Print VPlan after construction and initial optimizations. NFC (PR #187443)

[Luke Lau via llvm-commits]

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@@ -8025,6 +8025,9 @@ VPRecipeBuilder::tryToCreateWidenNonPhiRecipe(VPSingleDefRecipe *R,
   return tryToWiden(VPI);
 }
 
+// To make RUN_VPLAN_PASS print initial VPlan.
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lukel97 wrote:

```suggestion
// To allow RUN_VPLAN_PASS to print the optimized VPlan.
```

https://github.com/llvm/llvm-project/pull/187443