[llvm] [VPlan] Support VPWidenCastRecipe in isSingleScalar. (PR #143552)

[Ramkumar Ramachandra via llvm-commits]

https://github.com/artagnon commented:

I had a similar patch at https://github.com/llvm/llvm-project/pull/162340, but @fhahn pointed out the regression. I now see your follow-up, and probably we can merge that with tweaks?

https://github.com/llvm/llvm-project/pull/143552