Import grouping order is inconsistent with import sorting order

With group_imports set to StdExternalCrate, Rustfmt will convert

use crate::a;
use super::b;
use self::c;
use itertools::d;
use std::e;

to

use std::e;

use itertools::d;

use self::c;
use super::b;
use crate::a;

The import groups are ordered from most general to most local, but self, super and crate are sorted in the other direction.

The import grouping order makes most sense to me. I'd suggest that when group_imports is StdExternalCrate, the order of crate, super and self should be reversed, giving a nice general → local order, thus:

use std::e;

use itertools::d;

use crate::a;
use super::b;
use self::c;

Or perhaps crate, super and self ought to get their own groups, though perhaps not, as they're less common than std and external/workspace imports in my experience. (Our code-base is 25 % std, 35 % external, 15 % workspace, 10 % crate, 10 % super and 5 % self, including tests but excluding documentation examples.)

No source file or test is named. Start by locating rustfmt's import grouping and sorting implementation, then compare the existing StdExternalCrate behavior with the ordering shown in the issue; done means a regression test and formatter output that consistently order std, external, crate, super, and self from general to local.