Should not visual-align same-line comments within function arguments

Sample code:

fn main() {
    w(
        thing,
        0, // thing2
        thing3,
        long_thing4, // acomment
        long_thing4, // bcomment
        long_thing4, // ccomment
        0, // another
        0, // comment
        thing5,
        long_thing6,
        thing7,
        0, // yet another comment
    );
}

rustfmt turns this into:

fn main() {
    w(
        thing,
        0, // thing2
        thing3,
        long_thing4, // acomment
        long_thing4, // bcomment
        long_thing4, // ccomment
        0,           // another
        0,           // comment
        thing5,
        long_thing6,
        thing7,
        0, // yet another comment
    );
}

Notice that // another and // comment got indented to visually align with the previous three comments.

This has multiple issues:

1. rustfmt should not, in general, be visually aligning anything; its defaults normally block-align everything, per https://github.com/rust-dev-tools/fmt-rfcs/issues/8 .
2. In this specific case, rustfmt has made the code less readable by doing so, moving comments away from the code they comment (0,) to align it with an unrelated comment, while leaving other comments in the same function call untouched. The alignment misleadingly suggests some relationship between the comments or the arguments, which doesn't exist.

I would expect rustfmt to always leave same-line comments one space away from the code they comment.

Start by reproducing the issue's Rust sample with rustfmt and compare the shown output. Trace the formatter's same-line comment alignment behavior, then verify that comments remain one space from their associated code without aligning to unrelated comments. Add or update coverage for this example and run the relevant rustfmt tests.