Revise destination name generation mechanism when building outlines

Previously, prefix was duplicated which resulted in named like
"pdfHTML-iText-outline-pdfHTML-iText-outline-1"

DEVSIX-3495

Author: Snipx

src/main/java/com/itextpdf/html2pdf/attach/impl/OutlineHandler.java

@@ -214,7 +214,7 @@ public String getDestinationNamePrefix() {
      * @return the unique destination name
      */
     protected String generateUniqueDestinationName(IElementNode element) {
-        return destinationNamePrefix + getUniqueID(destinationNamePrefix);
+        return getUniqueID(destinationNamePrefix);
     }
 
     /**

src/test/java/com/itextpdf/html2pdf/attach/impl/OutlineHandlerTest.java

@@ -69,7 +69,7 @@ public void defaultDestinationPrefixTest() {
         PdfOutline pdfOutline = context.getPdfDocument().getOutlines(false).getAllChildren().get(0);
         Assert.assertEquals("p1", pdfOutline.getTitle());
         PdfString pdfStringDest = (PdfString) pdfOutline.getDestination().getPdfObject();
-        Assert.assertEquals("pdfHTML-iText-outline-pdfHTML-iText-outline-1", pdfStringDest.toUnicodeString());
+        Assert.assertEquals("pdfHTML-iText-outline-1", pdfStringDest.toUnicodeString());
     }
 
     @Test
@@ -96,6 +96,6 @@ public void customDestinationPrefixTest() {
         PdfOutline pdfOutline = context.getPdfDocument().getOutlines(false).getAllChildren().get(0);
         Assert.assertEquals("p1", pdfOutline.getTitle());
         PdfString pdfStringDest = (PdfString) pdfOutline.getDestination().getPdfObject();
-        Assert.assertEquals("prefix-prefix-1", pdfStringDest.toUnicodeString());
+        Assert.assertEquals("prefix-1", pdfStringDest.toUnicodeString());
     }
 }