Separate a reusable Image class from Screen (#834)

Co-authored-by: ArthurSonzogni <sonzogniarthur@gmail.com>

include/ftxui/screen/image.hpp

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+// Copyright 2024 Arthur Sonzogni. All rights reserved.
+// Use of this source code is governed by the MIT license that can be found in
+// the LICENSE file.
+#ifndef FTXUI_SCREEN_IMAGE_HPP
+#define FTXUI_SCREEN_IMAGE_HPP
+
+#include <cstdint>  // for uint8_t
+#include <memory>
+#include <string>  // for string, basic_string, allocator
+#include <vector>  // for vector
+
+#include "ftxui/screen/box.hpp"    // for Box
+#include "ftxui/screen/pixel.hpp"  // for Pixel
+
+namespace ftxui {
+
+/// @brief A rectangular grid of Pixel.
+/// @ingroup screen
+class Image {
+ public:
+  // Constructors:
+  Image() = delete;
+  Image(int dimx, int dimy);
+
+  // Access a character in the grid at a given position.
+  std::string& at(int x, int y);
+  const std::string& at(int x, int y) const;
+
+  // Access a cell (Pixel) in the grid at a given position.
+  Pixel& PixelAt(int x, int y);
+  const Pixel& PixelAt(int x, int y) const;
+
+  // Get screen dimensions.
+  int dimx() const { return dimx_; }
+  int dimy() const { return dimy_; }
+
+  // Fill the image with space and default style
+  void Clear();
+
+  Box stencil;
+
+ protected:
+  int dimx_;
+  int dimy_;
+  std::vector<std::vector<Pixel>> pixels_;
+};
+
+}  // namespace ftxui
+
+#endif  // FTXUI_SCREEN_IMAGE_HPP