LibJS: Throw when new is used on non-constructor methods

[BinaryAlley]

Non-constructor methods and plain object methods were incorrectly treated as constructors when used with "new", resulting in a new Object instance instead of throwing a TypeError. Example:

// ok: class constructor
class OK { constructor() {} }
const ok = new OK();
new ok.constructor;

// should throw: instance method
class FAIL { m() {} }
const fail = new FAIL();
new fail.m;

// should throw: method on object literal
new ({ m() {} }).m;

// should throw: function expression used as object property
new ({ b: function () { this.x = 2; } }).b();

// should throw: extracted class method used with new
const m = class { m() {} }.prototype.m;
new m;

Fixes #6926

[gmta]

Welcome! Can you add some of those examples to a regression test?

[BinaryAlley]

Thank you! I'll attempt to do so.

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