Fix auto-import barrel ranking for path-prefix collisions

[Copilot]

Auto-import incorrectly penalized an index barrel when its directory name was a textual prefix of the importing file name:

/utils/sum/index.ts
/utils/sumAB.ts

• Root cause: Circular-import detection used a plain string-prefix check, treating sumAB.ts as contained by sum/.
• Change: Require a path-segment boundary when checking directory containment.
• Coverage: Add a NodeNext fourslash regression test verifying both barrel and direct ESM import paths are offered in the correct order.

• Fixes Auto-import ignores barrel (index.ts) when the imported folder name is a prefix of the importing file name #64029

[Copilot]

Pull request overview

Fixes auto-import barrel ranking when a directory name prefixes the importing filename.

Changes:

• Requires a directory boundary in the cycle heuristic.
• Adds NodeNext ESM regression coverage for ordering.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
tsc/internal/ls/autoimport/fix.go	Corrects directory containment detection.
tsc/internal/fourslash/tests/autoImportIndexReExportPrefix_test.go	Verifies barrel and direct import ordering.

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