LibJS: Implement Error function/constructor

Author: https://github.com/linusg
Commit: ee6472fef2
Pull-request: https://github.com/SerenityOS/serenity/pull/1568

Libraries/LibJS/Tests/Error.js

@@ -0,0 +1,29 @@
+function assert(x) { if (!x) throw 1; }
+
+try {
+    var e;
+
+    e = Error();
+    assert(e.name === "Error");
+    assert(e.message === "");
+
+    e = Error(undefined);
+    assert(e.name === "Error");
+    assert(e.message === "");
+
+    e = Error("test");
+    assert(e.name === "Error");
+    assert(e.message === "test");
+
+    e = Error(42);
+    assert(e.name === "Error");
+    assert(e.message === "42");
+
+    e = Error(null);
+    assert(e.name === "Error");
+    assert(e.message === "null");
+
+    console.log("PASS");
+} catch (e) {
+    console.log("FAIL: " + e);
+}