LibJS: Implement basic execution of "switch" statements

The "break" keyword now unwinds to the nearest ScopeType::Breakable.
There's no support for break labels yet, but we'll get there too.

Libraries/LibJS/Tests/switch-basic-2.js

@@ -0,0 +1,10 @@
+var a = "foo";
+
+switch (a + "bar") {
+case 1:
+	break;
+case "foobar":
+case 2:
+        console.log("PASS");
+	break;
+}