(core) Nice summary table IDs

Summary:
Changes auto-generated summary table IDs from e.g. `GristSummary_6_Table1` to `Table1_summary_A_B` (meaning `Table1` grouped by `A` and `B`). This makes it easier to write formulas involving summary tables, make API requests, understand logs, etc.

Because these don't encode the source table ID as reliably as before, `decode_summary_table_name` now uses the summary table schema info, not just the summary table ID. Specifically, it looks at the type of the `group` column, which is `RefList:<source table id>`.

Renaming a source table renames the summary table as before, and now renaming a groupby column renames the summary table as well.

Conflicting table names are resolved in the usual way by adding a number at the end, e.g. `Table1_summary_A_B2`. These summary tables are not automatically renamed when the disambiguation is no longer needed.

A new migration renames all summary tables to the new scheme, and updates formulas using summary tables with a simple regex.

Test Plan:
Updated many tests to use the new style of name.

Added new Python tests to for resolving conflicts when renaming source tables and groupby columns.

Added a test for the migration, including renames in formulas.

Reviewers: georgegevoian

Reviewed By: georgegevoian

Differential Revision: https://phab.getgrist.com/D3508

sandbox/grist/engine.py

@@ -436,7 +436,7 @@ class Engine(object):
     m = match_counter.MatchCounter(sample)
     # Iterates through each valid column in the document, counting matches.
     for c in search_cols:
-      if (not gencode._is_special_table(c.tableId) and
+      if (not (gencode._is_special_table(c.tableId) or c.parentId.summarySourceTable) and
           column.is_visible_column(c.colId) and
           not c.type.startswith('Ref')):
         table = self.tables[c.tableId]
@@ -1265,7 +1265,7 @@ class Engine(object):
     return sum(
       table._num_rows()
       for table_id, table in six.iteritems(self.tables)
-      if useractions.is_user_table(table_id)
+      if useractions.is_user_table(table_id) and not table._summary_source_table
     )
 
   def apply_user_actions(self, user_actions, user=None):