[llvm] [VPlan] Re-use VPSlotTracker when printing recipes for costs (NFC). (PR #203386)

[Luke Lau via llvm-commits]

https://github.com/lukel97 approved this pull request.

LGTM. I guess it's just the VPCostContext in `LoopVectorizationPlanner::tryToBuildVPlan` we need to be careful about. There's another call to VPCostContext's c-tor in `LoopVectorizePass::processLoop` that could probably also reuse the VPSlotTracker

https://github.com/llvm/llvm-project/pull/203386