Clean source code. Add to_wstring<T> T={int, float, double, ...}

examples/dom/frame.cpp

examples/dom/package_manager.cpp

ftxui/include/ftxui/component/input.hpp

ftxui/include/ftxui/component/menu.hpp

ftxui/include/ftxui/dom/elements.hpp

ftxui/include/ftxui/requirement.hpp

ftxui/include/ftxui/util/string.hpp

ftxui/src/ftxui/dom/gauge_test.cpp

ftxui/src/ftxui/dom/vbox_test.cpp