add standard comment to #endif's

Tests/UnitTests/gui2/libtestmachinery/folderbasedtest.h

Tests/UnitTests/gui2/libtestmachinery/google_test.h

Tests/UnitTests/gui2/libtestmachinery/test_utils.h

Tests/UnitTests/gui2/libtestmachinery/widgetbasedtest.h

gui2/sldeditor/sldviewwidget.h

mvvm/model/mvvm/interfaces/applicationmodelsinterface.h

mvvm/model/mvvm/serialization/jsondocument.h

mvvm/model/mvvm/utils/mathconstants.h

mvvm/tests/libtestmachinery/folderbasedtest.h

mvvm/tests/libtestmachinery/google_test.h

mvvm/tests/libtestmachinery/mockinterfaces.h

mvvm/tests/libtestmachinery/test_utils.h

mvvm/tests/libtestmachinery/widgetbasedtest.h

mvvm/tests/testview/customplot_test_utils.h

mvvm/view/mvvm/plotting/customplotproxywidget.h

mvvm/view/mvvm/widgets/allitemstreeview.h