Perf tuning: skip numberChildren

hapifhir#1699 Workaround for performance issue with FML transform: Growing/large lists getting very slow due to numberChildren() getting called recursively for every element that is added to a list.

merge upstream

org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/elementmodel/Element.java

@@ -563,7 +563,6 @@ public Element makeElement(String name) throws FHIRException {
         } else {
           Element ne = new Element(child).setFormat(format);
           children.add(ne);
-          numberChildren();
           return ne;
         }
       }
@@ -1648,4 +1647,4 @@ public void setElided(boolean elided) {
   public boolean isElided() {
     return this.elided;
   }
-}
+}