Enable `allowJs` with `isolatedDeclarations`

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Comment

Today, an error is issued when allowJs is set alongside isolatedDeclarations - js and ts .d.ts emit use the same pipeline, so it really should work, provided the error generation logic isn't making too many syntax assumptions.

Mostly, unlocking this is going to involve looking through the isolatedDeclarations tests and copying them with their cast/annotation syntaxes swapped to jsdoc and filenames swapped to .js just to give confidence things are going to work OK (and that getEffectiveTypeNode is being used over a direct .type get in enough places in the error generator). There's a few other JS-specific error cases to look at (js's unique export/expression merges, for one) that may need some new errors, but the bulk of it is just ensuring the existing type node presence checking logic generalizes to jsdoc-sourced type nodes.

Commencez par examiner les tests existants de isolatedDeclarations et le error generator, en particulier les utilisations de getEffectiveTypeNode par rapport à l’accès direct au type. Dupliquez les cas pertinents avec des annotations JSDoc et des noms de fichiers .js, puis étudiez les cas spécifiques à JavaScript d’exportation et de fusion d’expressions. C’est terminé lorsque allowJs avec isolatedDeclarations n’échoue plus à tort et que les tests étendus passent.