LibJS: Add Number.parseInt

This is initialized to be the same function object as the initial value
of the parseInt function on the global object.

Userland/Libraries/LibJS/Tests/builtins/Number/Number.parseInt.js

@@ -0,0 +1,5 @@
+test("basic functionality", () => {
+    // Ensuring it's the same function as the global
+    // parseInt() is enough as that already has tests :^)
+    expect(Number.parseInt).toBe(parseInt);
+});