javafx.css.SimpleSelector in javafx.css has been deprecated and marked for removal

[jperedadnr]

javafx.css.SimpleSelector and javafx.css.CompoundSelector are deprecated in 23, see https://bugs.openjdk.org/browse/JDK-8324182, and removed in 24-ea, see https://bugs.openjdk.org/browse/JDK-8323706.

These are used in Kit CSSInternal::getStyleClasses, and the fix should be simple, just using this code:

for (Rule r : s.getRules()) {
            for (Selector ss : r.getSelectors()) {
                styleClasses.addAll(ss.getStyleClassNames());
            }
        }