[llvm] [VPlan][UTC] Number VPlan passes' instances in printing/filtering (PR #211424)

[Andrei Elovikov via llvm-commits]

eas wrote:

> Do we actually need a new option for that? Could we instead just number the pass invocations and print them as something like `... VPlanTransforms::simplifyRecipes at 2` etc, potentially skipping `@1` which is redundant for most passes?
> 
> That would also make it slightly easier to see what `vplan-print-after` to add instead of manually counting

Thanks, like this suggestion! Implemented in the latest upload. Skipping `@1` (done there) results in less tests changed (existing `-vplan-print-after=optimize$` RUN lines work unmodified) and the inconsistency is probably not too bad.

https://github.com/llvm/llvm-project/pull/211424