[llvm] [LV][NFC] Use APFloat class when printing out costs per lane (PR #201824)

[David Sherwood via llvm-commits]

david-arm wrote:

In order to make this patch more manageable I've pulled in changes from https://github.com/llvm/llvm-project/pull/201560 to help auto-generate the CHECK lines in the WebAssembly test, since the new printing format causes a large number of test failures.

https://github.com/llvm/llvm-project/pull/201824