Prefer index barrels for relative auto-imports

[Copilot]

Auto-import source selection used alphabetical ordering to break ties between direct files and index.ts barrels, producing inconsistent imports based on filename casing and spelling.

• Ranking

  • Prefer index-file re-exports among otherwise-equivalent relative candidates.
  • Preserve path-depth ranking, cycle avoidance, and ambient/package import behavior.

• Coverage

  • Add a NodeNext regression case where double.ts previously outranked index.ts.
  • Update existing barrel-order expectations.

// Before
import { double } from "./utils/double/double.js";

// Preferred
import { double } from "./utils/double/index.js";

• Fixes Auto-import prioritizes files alphabetically before index.ts inside a folder, ignoring the barrel #64034