LibJS: Add basic Array constructor

We only support Array() with 0 or 1 parameters so far.

Libraries/LibJS/Tests/Array.js

@@ -0,0 +1,16 @@
+function assert(x) { if (!x) throw 1; }
+
+try {
+    assert(Array.length === 1);
+    assert(Array.prototype.length === 0);
+    assert(typeof Array() === "object");
+    assert(typeof new Array() === "object");
+
+    x = new Array(5);
+
+    assert(x.length === 5);
+
+    console.log("PASS");
+} catch (e) {
+    console.log("FAIL: " + e.message);
+}