Remove `print::Pat` from the printing of `WitnessPat` After the preliminary work done in #128536, we can now get rid of `print::Pat` entirely. - First, we introduce a variant `PatKind::Print(String)`. - Then we incrementally remove each other variant of `PatKind`, by having the relevant code produce `PatKind::Print` instead. - Once `PatKind::Print` is the only remaining variant, it becomes easy to remove `print::Pat` and replace it with `String`. There is more cleanup that I have in mind, but this seemed like a natural stopping point for one PR. r? ```@Nadrieril```