(core) Add a row to summary tables grouped by list column(s) corresponding to empty lists

Summary:
Adds some special handling to summary table and lookup logic:

- Source rows with empty choicelists/reflists get a corresponding summary row with an empty string/reference when grouping by that column, instead of excluding them from any group
- Adds a new `QueryOperation` 'empty' in the client which is used in `LinkingState`, `QuerySet`, and `recursiveMoveToCursorPos` to match empty lists in source tables against falsy values in linked summary tables.
- Adds a new parameter `match_empty` to the Python `CONTAINS` function so that regular formulas can implement the same behaviour as summary tables. See https://grist.slack.com/archives/C0234CPPXPA/p1654030490932119
- Uses the new `match_empty` argument in the formula generated for the `group` column when detaching a summary table.

Test Plan: Updated and extended Python and nbrowser tests of summary tables grouped by choicelists to test for new behaviour with empty lists.

Reviewers: georgegevoian

Reviewed By: georgegevoian

Differential Revision: https://phab.getgrist.com/D3471

sandbox/grist/docmodel.py

@@ -9,10 +9,10 @@ import itertools
 
 import six
 
+import functions
 import records
 import usertypes
 import relabeling
-import lookup
 import table
 import moment
 from schema import RecalcWhen
@@ -31,7 +31,7 @@ def _record_ref_list_set(table_id, group_by, sort_by=None):
   @usertypes.formulaType(usertypes.ReferenceList(table_id))
   def func(rec, table):
     lookup_table = table.docmodel.get_table(table_id)
-    return lookup_table.lookupRecords(sort_by=sort_by, **{group_by: lookup._Contains(rec.id)})
+    return lookup_table.lookupRecords(sort_by=sort_by, **{group_by: functions.CONTAINS(rec.id)})
   return func