Feature: hscroll_indicator (#753)

This is the symetrical of `vscroll_indicator`.

Requested by @ibrahimnasson.

Fixed:https://github.com/ArthurSonzogni/FTXUI/issues/752

examples/component/CMakeLists.txt

@@ -25,6 +25,7 @@ example(menu2)
 example(menu_entries)
 example(menu_entries_animated)
 example(menu_in_frame)
+example(menu_in_frame_horizontal)
 example(menu_multiple)
 example(menu_style)
 example(menu_underline_animated_gallery)

examples/component/menu_in_frame_horizontal.cpp

@@ -0,0 +1,30 @@
+// Copyright 2020 Arthur Sonzogni. All rights reserved.
+// Use of this source code is governed by the MIT license that can be found in
+// the LICENSE file.
+#include <memory>  // for shared_ptr, __shared_ptr_access
+#include <string>  // for string, basic_string, operator+, to_string
+#include <vector>  // for vector
+
+#include "ftxui/component/captured_mouse.hpp"      // for ftxui
+#include "ftxui/component/component.hpp"           // for Radiobox, Renderer
+#include "ftxui/component/component_base.hpp"      // for ComponentBase
+#include "ftxui/component/screen_interactive.hpp"  // for ScreenInteractive
+#include "ftxui/dom/elements.hpp"  // for operator|, Element, size, border, frame, HEIGHT, LESS_THAN
+
+using namespace ftxui;
+
+int main() {
+  std::vector<std::string> entries;
+  int selected = 0;
+
+  for (int i = 0; i < 100; ++i)
+    entries.push_back(std::to_string(i));
+  auto radiobox = Menu(&entries, &selected, MenuOption::Horizontal());
+  auto renderer = Renderer(
+      radiobox, [&] { return radiobox->Render() | hscroll_indicator | frame; });
+
+  auto screen = ScreenInteractive::FitComponent();
+  screen.Loop(renderer);
+
+  return 0;
+}