[builtins] Migrate escape/unescape from uri.js to C++.

src/uri.h

Index: src/uri.h
diff --git a/src/uri.h b/src/uri.h
index cb223bd63d1e6c20126dbbca173ba5bd9b3285a4..dfa057fd09c3b13cdc8ee4c4312d938086274d63 100644
--- a/src/uri.h
+++ b/src/uri.h
@@ -35,6 +35,12 @@ class Uri : public AllStatic {
     return Encode(isolate, component, false);
   }
 
+  // ES6 section B.2.1.1 escape (string)
+  static MaybeHandle<String> Escape(Isolate* isolate, Handle<String> string);
+
+  // ES6 section B.2.1.2 unescape (string)
+  static MaybeHandle<String> Unescape(Isolate* isolate, Handle<String> string);
+
  private:
   static MaybeHandle<String> Decode(Isolate* isolate, Handle<String> uri,
                                     bool is_uri);