8$: report E0429 for class 'extends' clause

[strager]

The following TypeScript code is invalid, but quick-lint-js accepts it without any diagnostic:

export class D<T> {}
export class D2 extends D<<U>() => number> {}

quick-lint-js should report E0429 like it does for implements and interface ... extends.

[skdoosh]

@strager please close this issue as it has been solved by @arieldon in the pr in the conversation above.