gh-36246: Use URLs to online Sage documents for JupyterLab
    
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Sage documents in the Help menu of JupyterLab have stopped working for
long time. Those are essentially links to local files, but they don't
work for JupyterLab. We replace them with URLs to online documents, to
make them functional again.

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URL: #36246
Reported by: Kwankyu Lee
Reviewer(s): Eric Gourgoulhon

Author: Release Manager

src/sage/repl/ipython_kernel/kernel.py

@@ -94,54 +94,68 @@ def help_links(self):
 
         See the Jupyter documentation.
 
-        .. NOTE::
-
-            Urls starting with "kernelspecs" are prepended by the
-            browser with the appropriate path.
-
         EXAMPLES::
 
             sage: from sage.repl.ipython_kernel.kernel import SageKernel
             sage: sk = SageKernel.__new__(SageKernel)
             sage: sk.help_links
             [{'text': 'Sage Documentation',
-              'url': 'kernelspecs/sagemath/doc/html/en/index.html'},
+              'url': 'https://doc.sagemath.org/html/en/index.html'},
              ...]
         """
+        # DEPRECATED: The URLs in the form 'kernelspecs/...' were used for
+        # classical Jupyter notebooks. For instance,
+        #
+        #  'kernelspecs/sagemath/doc/html/en/index.html'
+        #
+        # is constructed by kernel_url('doc/html/en/index.html'), but these
+        # URLs of local files don't work for JupyterLab. Hence all URLs here
+        # have been replaced with URLs of online documents.
+
         from sage.repl.ipython_kernel.install import SageKernelSpec
         identifier = SageKernelSpec.identifier()
 
         def kernel_url(x):
+            # URLs starting with 'kernelspecs' are prepended by the
+            # browser with the appropriate path
             return 'kernelspecs/{0}/{1}'.format(identifier, x)
 
         return [
             {
                 'text': 'Sage Documentation',
-                'url': kernel_url('doc/html/en/index.html'),
+                'url': "https://doc.sagemath.org/html/en/index.html",
+            },
+            {
+                'text': 'A Tour of Sage',
+                'url': "https://doc.sagemath.org/html/en/a_tour_of_sage/index.html",
             },
             {
                 'text': 'Tutorial',
-                'url': kernel_url('doc/html/en/tutorial/index.html'),
+                'url': "https://doc.sagemath.org/html/en/tutorial/index.html",
             },
             {
                 'text': 'Thematic Tutorials',
-                'url': kernel_url('doc/html/en/thematic_tutorials/index.html'),
+                'url': "https://doc.sagemath.org/html/en/thematic_tutorials/index.html",
             },
             {
-                'text': 'FAQs',
-                'url': kernel_url('doc/html/en/faq/index.html'),
+                'text': 'PREP Tutorials',
+                'url': "https://doc.sagemath.org/html/en/prep/index.html",
             },
             {
-                'text': 'PREP Tutorials',
-                'url': kernel_url('doc/html/en/prep/index.html'),
+                'text': 'Constructions',
+                'url': "https://doc.sagemath.org/html/en/constructions/index.html",
+            },
+            {
+                'text': 'FAQ',
+                'url': "https://doc.sagemath.org/html/en/faq/index.html",
             },
             {
                 'text': 'Reference',
-                'url': kernel_url('doc/html/en/reference/index.html'),
+                'url': "https://doc.sagemath.org/html/en/reference/index.html",
             },
             {
                 'text': "Developer's Guide",
-                'url': kernel_url('doc/html/en/developer/index.html'),
+                'url': "https://doc.sagemath.org/html/en/developer/index.html",
             },
             {
                 'text': "Python",