LibJS: Implement exponentiation (** operator)

Libraries/LibJS/Tests/exponentiation-basic.js

@@ -0,0 +1,30 @@
+function assert(x) { if (!x) throw 1; }
+
+try {
+    assert(2 ** 0 === 1);
+    assert(2 ** 1 === 2);
+    assert(2 ** 2 === 4);
+    assert(2 ** 3 === 8);
+    assert(2 ** -3 === 0.125);
+    assert(3 ** 2 === 9);
+    assert(0 ** 0 === 1);
+    assert(2 ** 3 ** 2 === 512);
+    assert(2 ** (3 ** 2) === 512);
+    assert((2 ** 3) ** 2 === 64);
+    assert("2" ** "3" === 8);
+    assert("" ** [] === 1);
+    assert([] ** null === 1);
+    assert(null ** null === 1);
+    assert(undefined ** null === 1);
+    assert(isNaN(NaN ** 2));
+    assert(isNaN(2 ** NaN));
+    assert(isNaN(undefined ** 2));
+    assert(isNaN(2 ** undefined));
+    assert(isNaN(null ** undefined));
+    assert(isNaN(2 ** "foo"));
+    assert(isNaN("foo" ** 2));
+
+    console.log("PASS");
+} catch (e) {
+    console.log("FAIL: " + e);
+}