WritableStream is missing close() method

[RReverser]

Upstream definition - https://streams.spec.whatwg.org/#writablestream - has a separate close() method, but TypeScript definition doesn't provide it (perhaps simply outdated).

[saschanaz]

Added by #1034

@github-actions close

[github-actions]

Closing because @saschanaz is one of the code-owners of this repository.