[llvm] [VPlan] Use EMIT-SCALAR when printing single-scalar VPInstructions. (PR #141428)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

> Should the VPInstructionWithType print changes also be included in this? https://github.com/llvm/llvm-project/commit/9c1a5dfda631447a7ff1cd293d8f68cd28765fd5#diff-34abe4c3cd34aa7a9664bbd204834248455635ba80b8a9ba9506d8c3e6b94d95R1084-R1090

I've left that out of the initial PR because currently we don't return true from isSingleScalar for any VPInstWithType. Will update in follow-ups to make sure this is consistently done

https://github.com/llvm/llvm-project/pull/141428