doc: document stream.isDestroyed()

`stream.isDestroyed()` has been exported since v19.9.0 but was never
documented, while its siblings `isErrored()`, `isReadable()` and
`isWritable()` all have entries in `doc/api/stream.md`.

Unlike those, `isDestroyed()` rejects Web streams: it returns `null`
for anything that is not a Node.js stream. The accepted types are
therefore documented as `Readable|Writable|Duplex` rather than also
listing `ReadableStream`/`WritableStream`.

Refs: #45671
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Signed-off-by: YspritanHyzygy <yspritan@gmail.com>
PR-URL: #64789
Reviewed-By: Aviv Keller <me@aviv.sh>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Daeyeon Jeong <daeyeon.dev@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: 2 people

doc/api/stream.md

@@ -3120,6 +3120,19 @@ console.log(res); // prints 'HELLOWORLD'
 For convenience, the [`readable.compose(stream)`][] method is available on
 {Readable} and {Duplex} streams as a wrapper for this function.
 
+### `stream.isDestroyed(stream)`
+
+<!-- YAML
+added:
+  - v19.9.0
+  - v18.17.0
+-->
+
+* `stream` {Readable|Writable|Duplex}
+* Returns: {boolean|null} - Only returns `null` if `stream` is not a valid `Readable`, `Writable` or `Duplex`.
+
+Returns whether the stream has been destroyed.
+
 ### `stream.isErrored(stream)`
 
 <!-- YAML