doc: document TransformStream transformer.cancel option · nodejs/node@736ed8a

Original file line number	Diff line number	Diff line change
`@@ -1148,6 +1148,12 @@ await Promise.all([`
`1148`	`1148`
`1149`	`1149`	`<!-- YAML`
`1150`	`1150`	`added: v16.5.0`
	`1151`	`+changes:`
	`1152`	`+ - version:`
	`1153`	`+ - v21.5.0`
	`1154`	`+ - v20.14.0`
	`1155`	`+ pr-url: https://github.com/nodejs/node/pull/50126`
	`1156`	+ description: Supports the `cancel` transformer callback.
`1151`	`1157`	`-->`
`1152`	`1158`
`1153`	`1159`	* `transformer` {Object}
`@@ -1166,6 +1172,11 @@ added: v16.5.0`
`1166`	`1172`	`the transformation process.`
`1167`	`1173`	* `controller` {TransformStreamDefaultController}
`1168`	`1174`	* Returns: A promise fulfilled with `undefined`.
	`1175`	+ * `cancel` {Function} A user-defined function that is called when either the
	`1176`	+ readable side of the `TransformStream` is canceled or the writable side is
	`1177`	`+ aborted.`
	`1178`	+ * `reason` {any}
	`1179`	+ * Returns: A promise fulfilled with `undefined`.
`1169`	`1180`	* `readableType` {any} the `readableType` option is reserved for future use
`1170`	`1181`	and _must_ be `undefined`.
`1171`	`1182`	* `writableType` {any} the `writableType` option is reserved for future use