Elide bare side-effect imports in JS declaration emit

[Copilot]

The declaration transformer was preserving bare side-effect imports (e.g. import "fs";) in .d.ts output for JS source files. Strada's JS declaration path synthesizes declarations symbolically via resolver.getDeclarationStatementsForSourceFile and therefore never emits these — per the issue discussion, the agreed behavior is to keep eliding them so side-effect imports remain scoped to runtime emit only.

Changes

• internal/transformers/declarations/transform.go — In transformImportDeclaration, return nil for ImportClause == nil when the current source file is JS:

  if decl.ImportClause == nil {
      // import "mod" - possibly needed for side effects in TS files...
      if tx.state.currentSourceFile != nil && tx.state.currentSourceFile.IsJS() {
          return nil
      }
      return tx.Factory().UpdateImportDeclaration(...)
  }

  TS source files retain the existing behavior of preserving bare side-effect imports.

• Baselines — Updated to reflect the elision and converge with Strada:

  • nodeModulesAllowJsExportAssignment (module=node16/18/20/nodenext): file.d.ts now emits export {}; (synthesized for moduleness) instead of import "fs";.
  • jsDeclarationsExportForms / jsDeclarationsExportFormsErr (target=es2015): bare import "./xxx" lines removed from aggregating JS files.

The export = a reordering noted in the issue was already produced by current emit and is acknowledged in the thread as preferable (closer to original source); only the .js baselines needed refreshing for it.