(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/plugin/TableOperations.ts

@@ -18,8 +18,7 @@ export interface TableOperations {
   /**
    * Delete a record or records.
    */
-  destroy(recordId: Types.RecordId): Promise<Types.RecordId>;
-  destroy(recordIds: Types.RecordId[]): Promise<Types.RecordId[]>;
+  destroy(recordIds: Types.RecordId|Types.RecordId[]): Promise<void>;
 
   /**
    * Add or update a record or records.