OptimisticTypesPersistence should use java.util.Date, not java.sql.Date

The change for JDK-8046921 introduced a new utility class, OptimisticTypesPersistence, that makes use of a type in java.sql, java.sql.Date. This would appear to be a mistake, most likely by the IDE when automatically adding the import statements. I suspect that it should be "import java.util.Date".

Snippets below show the affected code, in OptimisticTypesPersistence.java:

    import java.sql.Date;
    ....

    private static String getVersionDirName() throws Exception {
         ....
         return "dev-" + new SimpleDateFormat("yyyyMMdd-HHmmss").format(new Date(getLastModifiedClassFile(dir, 0L)));
        ....
    }


This issue causes problems for modularity, as it creates a new dependency on a type in java.sql.