(core) Implement new representation of ACL rules.

Summary:
- Added fields to _grist_ACLRules for the new Granular ACL representation
- Include a corresponding migration.

- Added ACLPermissions module with merging PermissionSets and converting to/from string.
- Implemented parsing of ACL formulas and compiling them into JS functions.
- Add automatic parsing of ACL formulas when ACLRules are added or updated.
- Convert GranularAccess to load and interpret new-style rules.
- Convert ACL UI to load and save new-style rules.

For now, no attempt to do anything better on the server or UI side, only to
reproduce previous behavior.

Test Plan: Added unittests for new files; fixed those for existing files.

Reviewers: paulfitz

Reviewed By: paulfitz

Differential Revision: https://phab.getgrist.com/D2664

sandbox/grist/migrations.py

@@ -767,3 +767,12 @@ def migration20(tdset):
       'indentation': [1 if v.id in table_views_map else 0 for v in views]
     })
   ])
+
+@migration(schema_version=21)
+def migration21(tdset):
+  return tdset.apply_doc_actions([
+    add_column('_grist_ACLRules', 'aclFormulaParsed', 'Text'),
+    add_column('_grist_ACLRules', 'permissionsText', 'Text'),
+    add_column('_grist_ACLRules', 'rulePos', 'PositionNumber'),
+    add_column('_grist_ACLRules', 'userAttributes', 'Text'),
+  ])