Handle comments inside &&&-bulleted blocks better

[jaybosamiya-ms]

The interaction of comments and bulleted blocks previously caused surprising number of newlines to show up. This PR fixes this.

In particular, the following code is now considered correctly-formatted

fn foo() {
    // these should stay together
    &&& x
    &&& y
    // xy
    &&& xy
    // zzz
    &&& z
}

Previously, there would be unnecessary newlines added after every comment. This would happen because comments have a forced-hardline after them, while &&& (and |||) bullets have a forced hardline before them, causing the number of hardlines to double-up, leading to surprising looking code.

Example sub-optimal code with the old surprising behavior (issue reported by Johanna (@JoPolzin)):

---

Note: this particular change causes a single-line change to the Verus vstd snapshot, but still requires a tiny amount of coordination to prevent spurious CI failures there before releasing (should not block merging, just blocks release, and should likely bump the minor version, rather than just patch version).

[parno]

I'm impressed you could make this work with such a minor diff to lib.rs!

[jaybosamiya-ms]

Yeah given that the comment is at a non-local nesting, I was worried it'd be a fairly complex fix, but once I realized I could flatten things, the diff became a lot smaller than the previous prototype of this that I was working with :)

[JoPolzin]

This is actually beautifull. I love it. Thanks :)