Try and stabilize Reflect.scala sortInPlace

[lihaoyi]

Tries to fix the instability in https://github.com/com-lihaoyi/mill/actions/runs/12719802399/job/35460719291?pr=4272

It seems sortInPlaceWith uses Ordering.fromLessThan, which means it must return false when both sides are equal. The previous implementation returned true when both getDeclaringClass and getReturnType were equal, which violates that invariant and could possible cause that crash depending on how the sort executes