feat(js_interop_gen): support automatically generated WebIDL typings via dogfooded generator

[kevmoo]

Extracts and registers the automated WebIDL AST typings generator inside 'tool/update_webidl_bindings.dart'.
Implements an elegant, stateless AST Renamer & Traversal Pass inside 'transform.dart' mapping raw type definitions recursively to standard nomenclatures under strict non-nullable nullabilities, keyword translations, and custom class property injections.
Deduplicates implements declarations globally to prevent clashing superclass annotations, generating pristine clean bindings with zero compiler source modifications.

[gemini-code-assist]

Code Review

This pull request updates the JS interop generator to support dogfooding of WebIDL typings, introducing a renaming map, custom type nullability fixes, and generated bindings for webidl2. Key changes include AST updates, a new transformation pass, and generated Dart files for the interop API. Feedback on the changes highlights a critical compile-time error in the generated code due to void property overrides, which should be filtered out. Additionally, reviewers noted an abstraction leak from hardcoding WebIDL-specific types in the core AST library and suggested optimizing JS interop getters by removing redundant hasProperty checks.

[gemini-code-assist]

The generated webidl_api.dart contains several compile-time errors because subtypes (such as InterfaceMixin, CallbackInterface, Namespace, etc.) override properties from their super-interfaces (Node and Interfacelike) with a type of void (e.g., external void parent; and external void inheritance;). In Dart, void is not a compatible subtype of Node? or String?, resulting in static analysis and compilation failures.

Since properties of type void are useless in Dart anyway, we should completely filter them out during the transformation pass. This allows the generated classes to cleanly inherit the correct types (Node? parent and String? inheritance) from their super-interfaces.

        if (decl is TypeDeclaration) {
          // Remove useless properties of type 'void' to prevent compile-time override conflicts
          decl.properties.removeWhere((prop) {
            final type = prop.type;
            return type is BuiltinType && type.name == 'void';
          });

[gemini-code-assist]

Hardcoding specific WebIDL types like 'RHS' and 'ValueDescription' inside the core AST library (types.dart) is an abstraction leak. js_interop_gen is designed to be a general-purpose JS interop generator from TypeScript definitions, so its core AST nodes should remain completely generic and free of library-specific overrides.

Instead of hardcoding these inside types.dart, we should pass these overrides dynamically via TypeOptions or DeclarationOptions from transform.dart, or handle them during the transformation pass.

[gemini-code-assist]

Using hasProperty followed by getProperty results in two separate JS interop roundtrips for each getter access. We can optimize this by directly calling getProperty and checking if the returned value is of the expected type using isA<T>(). This is more efficient, idiomatic, and safer.

  bool get union {
    final jsObj = this as JSObject;
    final prop = jsObj.getProperty('union'.toJS);
    return prop.isA<JSBoolean>() ? (prop as JSBoolean).toDart : false;
  }

  String get generic {
    final jsObj = this as JSObject;
    final prop = jsObj.getProperty('generic'.toJS);
    return prop.isA<JSString>() ? (prop as JSString).toDart : '';
  }