Keep the W3CBuilder static

Ensures API backcompat

src/main/java/org/jsoup/helper/W3CDom.java

@@ -240,6 +240,7 @@ public void convert(org.jsoup.nodes.Document in, Document out) {
  */
  public void convert(org.jsoup.nodes.Element in, Document out) {
  W3CBuilder builder = new W3CBuilder(out);
+ builder.namespaceAware = namespaceAware;
  org.jsoup.nodes.Document inDoc = in.ownerDocument();
  if (inDoc != null) {
  if (!StringUtil.isBlank(inDoc.location())) {
@@ -333,11 +334,12 @@ public String asString(Document doc) {
  /**
  * Implements the conversion by walking the input.
  */
- protected class W3CBuilder implements NodeVisitor {
+ protected static class W3CBuilder implements NodeVisitor {
  private static final String xmlnsKey = "xmlns";
  private static final String xmlnsPrefix = "xmlns:";
 
  private final Document doc;
+ private boolean namespaceAware = true;
  private final Stack<HashMap<String, String>> namespacesStack = new Stack<>(); // stack of namespaces, prefix => urn
  private Node dest;
  private Syntax syntax = Syntax.xml; // the syntax (to coerce attributes to). From the input doc if available.