Add missing includes for gcc

examples/component/window.cpp

include/ftxui/screen/string.hpp

src/ftxui/component/container.cpp

src/ftxui/component/screen_interactive.cpp

src/ftxui/component/slider.cpp

src/ftxui/component/window.cpp

src/ftxui/dom/benchmark_test.cpp

src/ftxui/screen/color.cpp

src/ftxui/screen/string_internal.hpp

tools/license_headers.cpp