Add an option to wrap IIFEs in parenthesis

For #1307.

test/compress/wrap_iife.js

@@ -0,0 +1,33 @@
+wrap_iife: {
+    options = {
+        negate_iife: false,
+    }
+    beautify = {
+        wrap_iife: true,
+    }
+    input: {
+        (function() {
+            return function() {
+                console.log('test')
+            };
+        })()();
+    }
+    expect_exact: '(function(){return function(){console.log("test")}})()();'
+}
+
+wrap_iife_in_return_call: {
+    options = {
+        negate_iife: false,
+    }
+    beautify = {
+        wrap_iife: true,
+    }
+    input: {
+        (function() {
+            return (function() {
+                console.log('test')
+            })();
+        })()();
+    }
+    expect_exact: '(function(){return(function(){console.log("test")})()})()();'
+}