Multiple fixes: signed/unsigned, etc... (#600)

.clang-tidy

include/ftxui/component/event.hpp

include/ftxui/component/mouse.hpp

include/ftxui/util/ref.hpp

src/ftxui/component/animation.cpp

src/ftxui/component/animation_test.cpp

src/ftxui/component/button.cpp

src/ftxui/component/button_test.cpp

src/ftxui/component/collapsible_test.cpp

src/ftxui/component/container.cpp

src/ftxui/component/dropdown.cpp

src/ftxui/component/event.cpp

src/ftxui/component/hoverable_test.cpp

src/ftxui/component/input_test.cpp

src/ftxui/component/menu_test.cpp

src/ftxui/component/modal_test.cpp

src/ftxui/component/radiobox_test.cpp

src/ftxui/component/receiver_test.cpp

src/ftxui/component/resizable_split.cpp

src/ftxui/component/resizable_split_test.cpp