8263050: move HtmlDocletWriter.verticalSeparator to IndexWriter

Reviewed-by: prappo

src/jdk.javadoc/share/classes/jdk/javadoc/internal/doclets/formats/html/HtmlDocletWriter.java

@@ -2165,10 +2165,6 @@ public class HtmlDocletWriter {
         return localStylesheets;
     }
 
-    Content getVerticalSeparator() {
-        return HtmlTree.SPAN(HtmlStyle.verticalSeparator, Text.of("|"));
-    }
-
     public void addPreviewSummary(Element forWhat, Content target) {
         if (utils.isPreviewAPI(forWhat)) {
             Content div = HtmlTree.DIV(HtmlStyle.block);

src/jdk.javadoc/share/classes/jdk/javadoc/internal/doclets/formats/html/IndexWriter.java

@@ -370,4 +370,8 @@ public class IndexWriter extends HtmlDocletWriter {
                 .collect(Collectors.toList());
         contentTree.add(contents.join(getVerticalSeparator(), pageLinks));
     }
+
+    private Content getVerticalSeparator() {
+        return HtmlTree.SPAN(HtmlStyle.verticalSeparator, Text.of("|"));
+    }
 }