Trailing comments removed with rustfmt::skip

[dhardy]

Looks similar to #4028 but posting a new issue since that was apparently solved.

Given this file, test.rs:

// leading comment

#![rustfmt::skip]

fn main() {
    println!("main"); // commented
}

// post comment

running rustfmt test.rs results in this output:

// leading comment

#![rustfmt::skip]

fn main() {
    println!("main"); // commented
}

This is loss-of-information, especially considering we can't rely on git for roll-back (#3862).