Add API to iterate over all cache entries in a cache

{{groovy}}
def docInCache = new HashMap()
def cache = xwiki.getXWiki().store.cache;
def jcache = xwiki.getXWiki().getPrivateField(cache, "cache");
def items = jcache.getRoot().getChildren();
for (item in items) {
  for (child in item.getChildren()) {
    for (doc in child.getData().values()) {
      def key = (doc.language==null) ? "${doc.database}:${doc.fullName}" : "${doc.database}:${doc.fullName}:${doc.language}"
      docInCache.put(key, doc.version)
      // println "${key}: ${doc.version}"
    }
  }
 }
...