Fix newView link to use context-relative URL instead of rootURL

Fixes JENKINS-51291 / #22743

When Jenkins is behind a reverse proxy (e.g. nginx), the Jenkins Root URL
may be configured to the internal server URL for agent connectivity.
The 'New View' link in the view tab bar was using rootURL, causing it to
navigate to the internal URL instead of the proxy URL.

Use request.contextPath + owner.url instead of rootURL so the link
resolves relative to the current origin (proxy URL), while still
correctly targeting the owning ViewGroup's newView action for both
root, folders, and My Views. This also fixes SECURITY-1471 by removing
rootURL from the link, preventing javascript: injection via Root URL.

Made-with: Cursor

Author: sahilleth

core/src/main/resources/hudson/views/DefaultMyViewsTabBar/myViewTabs.jelly

@@ -30,7 +30,7 @@ THE SOFTWARE.
       <l:tab name="${v.displayName}" active="${v==currentView}" href="${rootURL}/${v.url}" />
     </j:forEach>
     <j:if test="${currentView.hasPermission(currentView.CREATE)}">
-      <l:tabNewItem href="${rootURL}/${currentView.owner.url}newView" title="${%New View}" />
+      <l:tabNewItem href="${request.contextPath}/${currentView.owner.url}newView" title="${%New View}" />
     </j:if>
   </l:tabBar>
 </j:jelly>

core/src/main/resources/hudson/views/DefaultViewsTabBar/viewTabs.jelly

@@ -41,7 +41,7 @@ THE SOFTWARE.
         </j:forEach>
 
         <j:if test="${currentView.hasPermission(currentView.CREATE)}">
-          <a href="${rootURL}/${currentView.owner.url}newView" tooltip="${%New View}" class="jenkins-button jenkins-button--tertiary">
+          <a href="${request.contextPath}/${currentView.owner.url}newView" tooltip="${%New View}" class="jenkins-button jenkins-button--tertiary">
             <l:icon src="symbol-add" />
           </a>
         </j:if>
@@ -53,7 +53,7 @@ THE SOFTWARE.
           <l:tab name="${v.displayName}" active="${v==currentView}" href="${rootURL}/${v.url}" />
         </j:forEach>
         <j:if test="${currentView.hasPermission(currentView.CREATE)}">
-          <l:tabNewItem href="${rootURL}/${currentView.owner.url}newView" title="${%New View}" />
+          <l:tabNewItem href="${request.contextPath}/${currentView.owner.url}newView" title="${%New View}" />
         </j:if>
       </l:tabBar>
     </j:otherwise>