doc: add isBigIntObject to documentation

Refs: nodejs#19989
Fixes: nodejs#55446
PR-URL: nodejs#55450
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>

doc/api/util.md

@@ -2379,6 +2379,24 @@ util.types.isBigInt64Array(new BigInt64Array());   // Returns true
 util.types.isBigInt64Array(new BigUint64Array());  // Returns false
 ```
 
+### `util.types.isBigIntObject(value)`
+
+<!-- YAML
+added: v10.4.0
+-->
+
+* `value` {any}
+* Returns: {boolean}
+
+Returns `true` if the value is a BigInt object, e.g. created
+by `Object(BigInt(123))`.
+
+```js
+util.types.isBigIntObject(Object(BigInt(123)));   // Returns true
+util.types.isBigIntObject(BigInt(123));   // Returns false
+util.types.isBigIntObject(123);  // Returns false
+```
+
 ### `util.types.isBigUint64Array(value)`
 
 <!-- YAML