Bug 1741148 - part 1: Rename nsINode::ComputeIndexOf to ComputeIndexOf_Deprecated r=smaug

It's hard to fix some callers.  Therefore, in this bug, we should fix only
simple cases.  Therefore, we should rename existing API first.

Differential Revision: https://phabricator.services.mozilla.com/D131334

dom/html/HTMLImageElement.cpp

@@ -60,7 +60,8 @@ static bool IsPreviousSibling(nsINode* aSubject, nsINode* aNode) {
 
   nsINode* parent = aSubject->GetParentNode();
   if (parent && parent == aNode->GetParentNode()) {
-    return parent->ComputeIndexOf(aSubject) < parent->ComputeIndexOf(aNode);
+    return parent->ComputeIndexOf_Deprecated(aSubject) <
+           parent->ComputeIndexOf_Deprecated(aNode);
   }
 
   return false;