Lint `overlapping_ranges_endpoints` directly instead of collecting into a Vec
In https://github.com/rust-lang/rust/pull/119396 I was a bit silly: I was trying to avoid any lints being fired from within the exhaustiveness algorithm for some vague aesthetic/reusability reason that doesn't really hold. This PR fixes that: instead of passing a `&mut Vec` around I just added a method to the `TypeCx` trait.
r? `@compiler-errors`