Prepare generator for `@webref/idl` 3.85+ and `@webref/css` 8+ (#594)

Updates `js_interop_gen` and `web_generator` to handle new WebIDL, CSS, and Browser Compat Data constructs in upcoming `@webref` and `@mdn` releases, with zero diff in `web/`:

- Resolve `[LegacyWindowAlias]` and `WindowProxy` type references to their canonical IDL declarations via `Translator.resolveIdlTypeName` across `_getRawType`, `_collectDocImports`, and `_getTypeNameRaw`, and assert against `[LegacyWindowAlias]` in `_setInheritance`.
- Prefix `[LegacyNamespace]` interfaces whose names shadow `dart:core` types (e.g. `WebAssembly.Exception` -> `WebAssemblyException` via `Translator.dartClassNameFor`) across declarations, references, `JSPromise<...>`, cross-file imports, union docs, and member-name collision checks while preserving `@JS('WebAssembly.Exception')`.
- Ignore `async_iterable` members, alias `async_sequence` to `JSObject`, support both `@webref/css` 6 and 7+ `listAll()` formats, and inspect all non-flagged/non-preview support statements in `bcd.dart`.
- Install `@latest` for `@webref/*` and `@mdn/browser-compat-data` in `web_generator/bin/update_idl_bindings.dart --update`.

Fixes #480