[Editor] Add the ability to create/update the structure tree when saving a pdf containing newly added annotations (bug 1845087)

When there is no tree, the tags for the new annotions are just put under the root element.
When there is a tree, we insert the new tags at the right place in using the value
of structTreeParentId (added in PR #16916).

src/core/primitives.js

@@ -262,6 +262,14 @@ class Dict {
 
     return mergedDict.size > 0 ? mergedDict : Dict.empty;
   }
+
+  clone() {
+    const dict = new Dict(this.xref);
+    for (const key of this.getKeys()) {
+      dict.set(key, this.getRaw(key));
+    }
+    return dict;
+  }
 }
 
 class Ref {