(core) Convert CopySelection and tableUtil to typescript

Summary:
- This should make these easier to work with and make changes to.
- Removes one unused method.

Test Plan: No changes of behavior, existing tests should pass.

Reviewers: alexmojaki

Reviewed By: alexmojaki

Differential Revision: https://phab.getgrist.com/D3091

app/client/components/DetailView.js

@@ -10,7 +10,7 @@ require('app/client/lib/koUtil'); // Needed for subscribeInit.
 
 var Base          = require('./Base');
 var BaseView      = require('./BaseView');
-var CopySelection = require('./CopySelection');
+var {CopySelection} = require('./CopySelection');
 var RecordLayout  = require('./RecordLayout');
 var commands      = require('./commands');
 const {RowContextMenu} = require('../ui/RowContextMenu');