LibJS: Hoist function declarations

This patch adds function declaration hoisting. The mechanism
is similar to var hoisting. Hoisted function declarations are to be put
before the hoisted var declarations, hence they have to be treated
separately.

Libraries/LibJS/Tests/function-hoisting.js

@@ -0,0 +1,37 @@
+load("test-common.js");
+
+try {
+    var callHoisted = hoisted();
+    function hoisted() {
+        return true;
+    }
+    assert(hoisted() === true);
+    assert(callHoisted === true);
+
+    {
+        var callScopedHoisted = scopedHoisted();
+        function scopedHoisted() {
+            return "foo";
+        }
+        assert(scopedHoisted() === "foo");
+        assert(callScopedHoisted === "foo");
+    }
+    assert(scopedHoisted() === "foo");
+    assert(callScopedHoisted === "foo");
+
+    const test = () => {
+        var iife = (function () {
+            return declaredLater();
+        })();
+        function declaredLater() {
+            return "yay";
+        }
+        return iife;
+    };
+    assert(typeof declaredLater === "undefined");
+    assert(test() === "yay");
+
+    console.log("PASS");
+} catch (e) {
+    console.log("FAIL: " + e);
+}