(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/summary.py

@@ -388,9 +388,11 @@ class SummaryActions(object):
     group_args = ', '.join(
       '%s=%s' % (
         c.summarySourceCol.colId,
-        'CONTAINS($%s)' % c.colId
-        if c.summarySourceCol.type.startswith(('ChoiceList', 'RefList:')) else
-        '$%s' % c.colId,
+        (
+          'CONTAINS($%s, match_empty="")' if c.summarySourceCol.type == 'ChoiceList' else
+          'CONTAINS($%s, match_empty=0)' if c.summarySourceCol.type.startswith('Reflist') else
+          '$%s'
+        ) % c.colId,
       )
       for c in field_col_recs if c.summarySourceCol
     )