Reject negative literals for unsigned or char types in pattern ranges and literals
It sucks a bit that we have to duplicate the work here (normal expressions just get this for free from the `ExprKind::UnOp(UnOp::Neg, ...)` typeck logic.
In https://github.com/rust-lang/rust/pull/134228 I caused
```rust
fn main() {
match 42_u8 {
-10..255 => {},
_ => {}
}
}
```
to just compile without even a lint.
I can't believe we didn't have tests for this
Amusingly https://github.com/rust-lang/rust/pull/136302 will also register a delayed bug in `lit_to_const` for this, so we'll have a redundancy if something like this fails again.
许杰友 Jieyou Xu (Joe)
f9f667f8b9