libui: Add Actions

This allows components like Buttons to take in capturing lambdas

libui/include/ui/Action.h

@@ -0,0 +1,68 @@
+#pragma once
+#include <luna/Heap.h>
+
+namespace ui
+{
+    class Action
+    {
+      public:
+        Action()
+        {
+            m_action = nullptr;
+        }
+
+        Action(Action&& other) : m_action(other.m_action)
+        {
+            other.m_action = nullptr;
+        }
+
+        template <typename T> Action(T&& function)
+        {
+            m_action = new (std::nothrow) ActionImpl<T>(move(function));
+        }
+
+        template <typename T> Action& operator=(T&& function)
+        {
+            if (m_action) delete m_action;
+            m_action = new (std::nothrow) ActionImpl<T>(move(function));
+            return *this;
+        }
+
+        void operator()()
+        {
+            check(m_action);
+            return m_action->call();
+        }
+
+        ~Action()
+        {
+            if (m_action) delete m_action;
+        }
+
+      private:
+        class ActionBase
+        {
+          public:
+            virtual void call() = 0;
+            virtual ~ActionBase() = default;
+        };
+
+        template <typename T> class ActionImpl final : public ActionBase
+        {
+          public:
+            ActionImpl(T&& function) : m_function(move(function))
+            {
+            }
+
+            void call()
+            {
+                return m_function();
+            }
+
+          private:
+            T m_function;
+        };
+
+        ActionBase* m_action;
+    };
+}