Feature: strikethrough and underlinedDouble decorator. (#561)

This resolves:
https://github.com/ArthurSonzogni/FTXUI/issues/560

src/ftxui/dom/strikethrough.cpp

@@ -0,0 +1,36 @@
+#include <memory>   // for make_shared
+#include <utility>  // for move
+
+#include "ftxui/dom/elements.hpp"        // for Element, strikethrough
+#include "ftxui/dom/node.hpp"            // for Node
+#include "ftxui/dom/node_decorator.hpp"  // for NodeDecorator
+#include "ftxui/screen/box.hpp"          // for Box
+#include "ftxui/screen/screen.hpp"       // for Pixel, Screen
+
+namespace ftxui {
+
+/// @brief Apply a strikethrough to text.
+/// @ingroup dom
+Element strikethrough(Element child) {
+  class Impl : public NodeDecorator {
+   public:
+    using NodeDecorator::NodeDecorator;
+
+    void Render(Screen& screen) override {
+      for (int y = box_.y_min; y <= box_.y_max; ++y) {
+        for (int x = box_.x_min; x <= box_.x_max; ++x) {
+          screen.PixelAt(x, y).strikethrough = true;
+        }
+      }
+      Node::Render(screen);
+    }
+  };
+
+  return std::make_shared<Impl>(std::move(child));
+}
+
+}  // namespace ftxui
+
+// Copyright 2023 Arthur Sonzogni. All rights reserved.
+// Use of this source code is governed by the MIT license that can be found in
+// the LICENSE file.

src/ftxui/dom/underlined_double.cpp

@@ -0,0 +1,36 @@
+#include <memory>   // for make_shared
+#include <utility>  // for move
+
+#include "ftxui/dom/elements.hpp"        // for Element, underlinedDouble
+#include "ftxui/dom/node.hpp"            // for Node
+#include "ftxui/dom/node_decorator.hpp"  // for NodeDecorator
+#include "ftxui/screen/box.hpp"          // for Box
+#include "ftxui/screen/screen.hpp"       // for Pixel, Screen
+
+namespace ftxui {
+
+/// @brief Apply a underlinedDouble to text.
+/// @ingroup dom
+Element underlinedDouble(Element child) {
+  class Impl : public NodeDecorator {
+   public:
+    using NodeDecorator::NodeDecorator;
+
+    void Render(Screen& screen) override {
+      for (int y = box_.y_min; y <= box_.y_max; ++y) {
+        for (int x = box_.x_min; x <= box_.x_max; ++x) {
+          screen.PixelAt(x, y).underlined_double = true;
+        }
+      }
+      Node::Render(screen);
+    }
+  };
+
+  return std::make_shared<Impl>(std::move(child));
+}
+
+}  // namespace ftxui
+
+// Copyright 2023 Arthur Sonzogni. All rights reserved.
+// Use of this source code is governed by the MIT license that can be found in
+// the LICENSE file.