[llvm] [LV] Reland "Add costs for VPInstructionWithType::computeCost" (PR #202952)

[David Sherwood via llvm-commits]

david-arm wrote:

> > I'm confused by the build failures. It works downstream. :(
> 
> Looks like [054a840](https://github.com/llvm/llvm-project/commit/054a840e0370704c9a9705f5660861f0364d08d8) landed on main which by coincidence also added the same VPInstructionWithType::computeCost overload, and the CI is testing the merge commit against main!

Ah ok. I'd better wait a day or two before landing this PR then because the original version of https://github.com/llvm/llvm-project/commit/054a840e0370704c9a9705f5660861f0364d08d8 caused buildbot failures. It would be a mess if that got reverted again with these changes added on top.

https://github.com/llvm/llvm-project/pull/202952