More fixes for socket stream close documentation

[wbamberg]

Follow-up to #40782 and #40789.

Main point being that you can't use the signal option to close an already-established connection, you can only use it to cancel a connection attempt before it has been established.

cc @tomayac .

This PR:

• updates the guide page at https://developer.mozilla.org/en-US/docs/Web/API/WebSockets_API/Using_WebSocketStream to give correct info about usage of signal and how to close a connection.
• adds some subheadings to the examples in https://developer.mozilla.org/en-US/docs/Web/API/WebSocketStream/WebSocketStream#examples, to make the structure clearer, and provides a bit of context for the stuff about closing a connection.

[github-actions]

Preview URLs

• /en-US/docs/Web/API/WebSocketStream/WebSocketStream
• /en-US/docs/Web/API/WebSocketStream/close
• /en-US/docs/Web/API/WebSockets_API/Using_WebSocketStream

External URLs (3)

URL: /en-US/docs/Web/API/WebSocketStream/close
Title: WebSocketStream: close() method

• https://developer.chrome.com/docs/capabilities/web-apis/websocketstream (1 time)
• https://github.com/whatwg/websockets/pull/48 (1 time)

---

URL: /en-US/docs/Web/API/WebSocketStream/WebSocketStream
Title: WebSocketStream: WebSocketStream() constructor

• https://github.com/whatwg/websockets/pull/48 (1 time) (Note! This may be a new URL 👀)

(comment last updated: 2025-08-21 02:16:45)

[tomayac]

Non-owner LGTM, thank you!