Add missing includes for gcc

Bug:https://github.com/ArthurSonzogni/FTXUI/issues/695

src/ftxui/screen/color.cpp

@@ -2,6 +2,7 @@
 
 #include <array>  // for array
 #include <cmath>
+#include <cstdint>
 #include <string_view>  // for literals
 
 #include "ftxui/screen/color_info.hpp"  // for GetColorInfo, ColorInfo

src/ftxui/screen/string_internal.hpp

@@ -1,6 +1,8 @@
 #ifndef FTXUI_SCREEN_STRING_INTERNAL_HPP
 #define FTXUI_SCREEN_STRING_INTERNAL_HPP
 
+#include <cstdint>
+
 namespace ftxui {
 
 bool EatCodePoint(const std::string& input,