(core) For autocomplete suggestions in formulas, add links to suggestions we have documentation for.

Summary:
This is a hacky solution that unfortunately relies on internal workings of ACE
autocomplete popups. I don't see a less hacky one if we stick with ACE
autocomplete.

Test Plan: Added a test case for links to test/nbrowser/Formulas.ts

Reviewers: paulfitz

Reviewed By: paulfitz

Differential Revision: https://phab.getgrist.com/D2610

sandbox/grist/test_completion.py

@@ -111,6 +111,11 @@ class TestCompletion(test_engine.EngineTestCase):
       ('Address.lookupRecords', '(colName=<value>, ...)', True),
     ])
 
+    self.assertEqual(self.engine.autocomplete("address.look", "Students"), [
+      ('Address.lookupOne', '(colName=<value>, ...)', True),
+      ('Address.lookupRecords', '(colName=<value>, ...)', True),
+    ])
+
   def test_suggest_column_type_methods(self):
     # Should treat columns as correct types.
     self.assertGreaterEqual(set(self.engine.autocomplete("$firstName.", "Students")),