Fix helpers emit for .cjs files in ESM module mode

[andrewbranch]

Noticed this while refactoring some code in Corsa.

[Copilot]

Pull Request Overview

This PR fixes the helpers emission for .cjs files when running in ESM module mode by refining the underlying logic and adding new test cases.

• Adds a new test case (ctsFileInEsnextHelpers.ts) and updates the expected baselines.
• Adjusts module specifier resolution by removing the fallback to the source file’s implied node format.
• Refines the condition for emitting external helper imports to better distinguish between CommonJS and ES module formats.

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

File	Description
tests/cases/compiler/ctsFileInEsnextHelpers.ts	Introduces a new test file for .cts files in ESM module mode.
tests/baselines/reference/ctsFileInEsnextHelpers.*	Updates baseline outputs (types, symbols, JS, errors) to reflect the new helper emit fix.
src/compiler/moduleSpecifiers.ts	Removes fallback to importingSourceFile.impliedNodeFormat, using overrideImportMode only.
src/compiler/factory/utilities.ts	Adjusts the condition for creating external helpers import to avoid CJS emission in ESM mode.

Comments suppressed due to low confidence (1)

src/compiler/moduleSpecifiers.ts:515

• Removing the fallback to 'importingSourceFile.impliedNodeFormat' might lead to undefined behavior when overrideImportMode is not set; consider explicitly handling the unset case to ensure the module specifier is resolved as intended.

options.overrideImportMode || importingSourceFile.impliedNodeFormat, 

[andrewbranch]

Before the change, emit was missing the tslib_1. on these

[andrewbranch]

I was able to simplify this condition in Corsa since we’re removing System, AMD, and UMD. Opting to make the minimal change here rather than try to clean up.