JDK regex compatibility

JDK9 has changed semantics of java.util.regex.Pattern in ways which are hard to predict and require us to essentially do a full analysis incoming XSD to map it reliably to Pattern – see https://bugs.openjdk.java.net/browse/JDK-8189343 .

I do not see any other recourse than to write a home-grown XSD regex parser, compliant with https://www.w3.org/TR/2004/REC-xmlschema-2-20041028/#regexs , which will produce an intermediate representation, which will then be translated to java.util.regex.Pattern language.