(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/lookup.py

@@ -198,6 +198,8 @@ class ContainsLookupMapColumn(BaseLookupMapColumn):
         # group = [] essentially means there are no new keys in this call
         if isinstance(group, (six.binary_type, six.text_type)):
           group = []
+        elif not group and col_id.match_empty != _Contains.no_match_empty:
+          group = [col_id.match_empty]
       else:
         group = [group]