(core) Improving custom widget API. Changing destroy function signature.

Summary:
Destroy function in TableOperations was throwing error when invoked with a single
record id instead of an array. Now it returns a void type.

Also changing mapColumns function signature as it doesn't require options for a default
behavior.

Test Plan: Updated tests.

Reviewers: alexmojaki

Reviewed By: alexmojaki

Differential Revision: https://phab.getgrist.com/D3404

app/server/lib/DocApi.ts

@@ -298,7 +298,8 @@ export class DocWorkerApi {
     this._app.post('/api/docs/:docId/tables/:tableId/data/delete', canEdit, withDoc(async (activeDoc, req, res) => {
       const rowIds = req.body;
       const op = getTableOperations(req, activeDoc);
-      res.json(await op.destroy(rowIds));
+      await op.destroy(rowIds);
+      res.json(null);
     }));
 
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