Fix JUnit HTML reports to preserve whitespace in failure messages

- Add `white-space: pre-wrap` CSS rule for `code` elements so spaces and
  newlines are preserved in browser rendering
- Wrap @message output in a `<code>` element so the failure message text
  also benefits from the whitespace preservation CSS rule

Fixes: #3723

Agent-Logs-Url: https://github.com/eclipse-platform/eclipse.platform.releng.aggregator/sessions/70ecfbb4-6cee-4f8f-a49b-c8496722fff2

Co-authored-by: Federico Jeanne <Federico.Jeanne@vector.com>

Author: Copilot

products/eclipse-junit-tests/src/main/scripts/JUNIT.XSL

@@ -97,6 +97,9 @@
       .Properties {
         text-align:right;
       }
+      code {
+        white-space: pre-wrap;
+      }
       </style>
       <script type="text/javascript" language="JavaScript">
         var TestCases = new Array();
@@ -572,7 +575,7 @@
     <xsl:choose>
         <xsl:when test="not(@message)">N/A</xsl:when>
         <xsl:otherwise>
-            <xsl:value-of select="@message"/>
+            <code><xsl:value-of select="@message"/></code>
         </xsl:otherwise>
     </xsl:choose>
     <!-- display the stacktrace -->