[generator] use a const set over a mutable list (#497)
| Package | Description | Version |
|---|---|---|
| web | Lightweight browser API bindings built around JS interop. |  |
| js_interop | Utility functions and types for dart:js_interop and dart:js_interop_unsafe. |  |
| web_generator | Tools to generate Dart interfaces from TypeScript declaration files and Web IDL definitions. | N/A |