Auto merge of #128146 - notriddle:notriddle/natsortfixes, r=GuillaumeGomez

rustdoc: clean up and fix ord violations in item sorting

Based on rust-lang/rust#128139 with a few minor changes:

- The name sorting function is changed to follow the [version sort] from the style guide
- the `cmp` function is redesigned to more obviously make a partial order, by always return `cmp()` of the same variable as the `!=` above

[version sort]: https://doc.rust-lang.org/nightly/style-guide/index.html#sorting

Author: bors