[llvm] [LV] Add initial costs for VPInstructionWithType::computeCost (PR #198291)

[Luke Lau via llvm-commits]

lukel97 wrote:

I'm seeing crashes with this patch building the MicroBenchmarks/all target on llvm-test-suite with `-target riscv64-linux-gnu -march=rva23u64 -O3`, it looks like an opcode is slipping through?

```
Unhandled opcode
UNREACHABLE executed at /Users/luke/Developer/llvm-project/llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp:1813!
```

Will work on a minimal reproducer

https://github.com/llvm/llvm-project/pull/198291