Rustfmt: [unstable option] reorder_impl_items

[scampi]

Tracking issue for unstable option: reorder_impl_items

[sum-elier]

Should reorganized elements maintain their original order?

Example:

pub trait MyTrait {
    type c;
    type b;
    type a;
}

So after formatting instead of this:

impl MyStruct for MyTrait {
   type a = ();
   type b = ();
   type c = ();
   ...
}

we have this:

impl MyStruct for MyTrait {
   type c = ();
   type b = ();
   type a = ();
   ...
}