(core) Add 'user' variable to trigger formulas

Summary:
The 'user' variable has a similar API to the one from access rules: it
contains properties about a user, such as their full name and email
address, as well as optional, user-defined attributes that are populated
via user attribute tables.

Test Plan: Python unit tests.

Reviewers: alexmojaki, paulfitz, dsagal

Reviewed By: alexmojaki, dsagal

Subscribers: paulfitz, dsagal, alexmojaki

Differential Revision: https://phab.getgrist.com/D2898

sandbox/grist/test_renames.py

@@ -309,18 +309,27 @@ class TestRenames(test_engine.EngineTestCase):
     ]})
 
   def test_rename_table_autocomplete(self):
+    user = {
+      'Name': 'Foo',
+      'UserID': 1,
+      'LinkKey': {},
+      'Origin': None,
+      'Email': 'foo@example.com',
+      'Access': 'owners'
+    }
+
     # Renaming a table should not leave the old name available for auto-complete.
     self.load_sample(self.sample)
     names = {"People", "Persons"}
     self.assertEqual(
-      names.intersection(self.engine.autocomplete("Pe", "Address", "city")),
+      names.intersection(self.engine.autocomplete("Pe", "Address", "city", user)),
       {"People"}
     )
 
     # Rename the table and ensure that "People" is no longer present among top-level names.
     out_actions = self.apply_user_action(["RenameTable", "People", "Persons"])
     self.assertEqual(
-      names.intersection(self.engine.autocomplete("Pe", "Address", "city")),
+      names.intersection(self.engine.autocomplete("Pe", "Address", "city", user)),
       {"Persons"}
     )