(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

app/common/ActiveDocAPI.ts

@@ -121,7 +121,10 @@ export interface QueryFilters {
   [colId: string]: any[];
 }
 
-export type QueryOperation = "in" | "intersects";
+// - in: value should be contained in filters array
+// - intersects: value should be a list with some overlap with filters array
+// - empty: value should be falsy (e.g. null) or an empty list, filters is ignored
+export type QueryOperation = "in" | "intersects" | "empty";
 
 /**
  * Response from useQuerySet(). A query returns data AND creates a subscription to receive