Fix the Button border and color with FlatStyle = Flat: FlatAppearance properties#13898

LeafShi1 wants to merge 2 commits intodotnet:maindotnet/winforms:mainfrom

LeafShi1:Fix_13897_Button_with_FlatAppearance_properties_in_DarModeLeafShi1/winforms:Fix_13897_Button_with_FlatAppearance_properties_in_DarModeCopy head branch name to clipboard