[feature request] add new `isPlainObject` predicate function

[DerekNonGeneric]

The isPlainObject predicate function is another common convenience function in the JS Object domain.

• It is quite frequently used and would be very helpful to have.
• It is distinct from the very similar isObject predicate function from @openinf/util-types
• It is distinct from the isObjectLike predicate function, which is often kept private/internal

---

const isPlainObject = ( obj ) => {
    return (
        typeof obj === 'object' &&
        obj !== null &&
        obj.constructor === Object &&
        Object.prototype.toString.call( obj ) === '[object Object]'
    );
};

---

Aside

hopefully not a misnomer due to the existence of [plain old Java objects (POJOs)](https://en.wikipedia.org/wiki/Plain_old_Java_object), which are [also a thing in JS](https://web.archive.org/web/20140913151352/http://ajaxian.com/archives/return-of-the-pojo-plain-ole-javascript)

Open question

would a more rigorous check be necessary to differentiate btwx the two or is it fine?

[DerekNonGeneric]

Very popular published packages for some prior art:

• is-plain-object: returns true only for objects created by the Object constructor
• isobject: returns true if the value is an object and not an array or null