(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

app/server/lib/DocPluginManager.ts

@@ -33,9 +33,10 @@ class GristDocAPIImpl implements GristDocAPI {
   public async getDocName() { return this._activeDoc.docName; }
 
   public async listTables(): Promise<string[]> {
-    const table = this._activeDoc.docData!.getMetaTable('_grist_Tables');
-    return table.getColValues('tableId')
-      .filter(id => !id.startsWith("GristSummary_")).sort();
+    return this._activeDoc.docData!.getMetaTable('_grist_Tables')
+      .getRecords()
+      .filter(r => !r.summarySourceTable)
+      .map(r => r.tableId);
   }
 
   public async fetchTable(tableId: string): Promise<TableColValues> {