Add missing preview feature checks to some java hints

[mbien]

Some hints didn't (correctly) check if the feature was supported by the source version / preview flag combination.

example:

NB 27 will suggest to convert this into a rule switch on JDK 17 (without preview enabled) which it shouldn't:

    public static void foo(Object obj) {
        if (obj instanceof Integer i) {
            System.out.println(i);
        } else if (obj instanceof Long l) {
            System.out.println(l);
        }
    }

(feature went final in 21)

[mbien]

will take another look today and make this a bit nicer. Planning to move the lang feature check into an enum, since the catch-all utility class is already large enough.

edit: done

[mbien]

I hoped I could use the enum from within the annotation, but I forgot that enum fields don't count as constants from javac's POV, since they are created during construction.

e.g this doesn't work:

@Hint(displayName = "#DN_ConvertToTextBlock", description = "#DESC_ConvertToTextBlock", category="rules15",
      minSourceVersion = Feature.TEXT_BLOCK.PREVIEW)

[lkishalmi]

Nice!

[lahodaj]

FWIW, makes sense to me, thanks!