[Feature request] Vertical formatting for attributes

Hi, it would be really cool if an attribute's content could be arranged in more ways. (Similar to array_width)

Example:

Currently, if you have this attribute:

#[diagnostic(
    code(...),
    url(...),
    severity(...)
)]
fn x() {...}

It will get rearranged to:

#[diagnostic(code(...), url(...), severity(...))]
fn x() {...}

It would be useful if there was an option specifically for vertical formatting in attributes' content

The issue names no source file, test, or entry point. Start by locating existing array_width handling in rustfmt's attribute-formatting code, then define the vertical-layout option and add coverage for the diagnostic example; done means the option reliably produces the requested vertical arrangement.