[llvm] [LAA] Switch safe-distance APIs to operate in elements instead of bits, NFCI'ish (PR #191867)

[Andrei Elovikov via llvm-commits]

eas wrote:

> No longer NFC'ish?

It's still changing

> Memory dependences are safe with a maximum safe vector width of 64 bits

into (for `i32` elements)

> Memory dependences are safe with a maximum safe number of elements to operate on equal to 2

so I'd say "NFC'ish" is applicable still.

https://github.com/llvm/llvm-project/pull/191867