Add code coverage support. (#378)

.github/workflows/build.yaml

CMakeLists.txt

cmake/ftxui_benchmark.cmake

cmake/ftxui_coverage.cmake

cmake/ftxui_test.cmake

src/ftxui/component/animation.cpp

src/ftxui/component/button.cpp

src/ftxui/component/component_test.cpp

src/ftxui/component/container_test.cpp

src/ftxui/component/input_test.cpp

src/ftxui/component/menu_test.cpp

src/ftxui/component/radiobox_test.cpp

src/ftxui/component/receiver_test.cpp

src/ftxui/component/screen_interactive_test.cpp

src/ftxui/component/terminal_input_parser_test.cpp

src/ftxui/dom/benchmark_test.cpp

src/ftxui/dom/flexbox_helper_test.cpp

src/ftxui/dom/flexbox_test.cpp

src/ftxui/dom/gauge_test.cpp

src/ftxui/dom/gridbox_test.cpp