[llvm] [LoopVectorize][NFC] Rewrite tests to check output of vplan cost model (PR #113697)

[David Sherwood via llvm-commits]

david-arm wrote:

> > Hi @fhahn, I'll merge this patch this morning, then teach the debug code to use the new helper function as part of PR #116247.
> 
> Sounds good, thought originally you wanted to merge #116247 first, but either order is fine

That was the original plan, but then I had trouble rebasing #116247 and that slowed things down. Plus I'm a bit nervous about delaying this patch for much longer otherwise I fear I'll forever be fixing up conflicts or failing tests. :)

https://github.com/llvm/llvm-project/pull/113697