Run IWYU. (#208)

examples/component/input.cpp

examples/component/menu_entries.cpp

examples/component/nested_screen.cpp

examples/dom/separator_style.cpp

include/ftxui/component/component.hpp

include/ftxui/component/component_options.hpp

include/ftxui/component/screen_interactive.hpp

include/ftxui/screen/color.hpp

iwyu.imp

src/ftxui/component/container.cpp

src/ftxui/component/menu.cpp

src/ftxui/dom/border.cpp

src/ftxui/dom/box_helper.cpp

src/ftxui/dom/box_helper.hpp

src/ftxui/dom/gauge.cpp

src/ftxui/dom/gridbox.cpp

src/ftxui/dom/gridbox_test.cpp

src/ftxui/dom/hbox.cpp

src/ftxui/dom/reflect.cpp

src/ftxui/dom/vbox.cpp