Userland: Change typedef to using directive

Problem:
- `typedef`s are read backwards making it confusing.
- `using` statements can be used in template aliases.
- `using` provides similarity to most other C++ syntax.

- C++ core guidelines say to prefer `using` over `typedef`:
  https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Rt-using

Solution:
- Switch these where appropriate.

Userland/DevTools/StateMachineGenerator/main.cpp

@@ -332,7 +332,7 @@ public:
     generator.append(R"~~~(
     }; // end Action
 
-    typedef Function<void(Action, u8)> Handler;
+    using Handler = Function<void(Action, u8)>;
 
     @class_name@(Handler handler)
     : m_handler(move(handler))