Execute IWYU (#299)

examples/component/canvas_animated.cpp

examples/component/collapsible.cpp

examples/component/focus.cpp

examples/dom/border.cpp

examples/dom/border_style.cpp

examples/dom/canvas.cpp

examples/dom/color_info_palette256.cpp

examples/dom/color_truecolor_HSV.cpp

examples/dom/color_truecolor_RGB.cpp

examples/dom/dbox.cpp

examples/dom/gauge.cpp

examples/dom/graph.cpp

examples/dom/gridbox.cpp

examples/dom/hflow.cpp

examples/dom/package_manager.cpp

examples/dom/separator.cpp

examples/dom/size.cpp

examples/dom/spinner.cpp

examples/dom/style_blink.cpp

examples/dom/style_bold.cpp