(core) Enabling clipboard events on Choice entry field

Summary: Copy/paste/cut events weren't available on choice entry field.

Test Plan: Updated tests

Reviewers: alexmojaki, paulfitz

Reviewed By: alexmojaki, paulfitz

Subscribers: alexmojaki

Differential Revision: https://phab.getgrist.com/D3476

app/client/widgets/ChoiceListEntry.ts

@@ -330,6 +330,9 @@ export class ChoiceListEntry extends Disposable {
         // Don't bubble up keyboard events, use them for editing the text.
         // Without this keys like Backspace, or Mod+a will propagate and modify all tokens.
         dom.on('keydown', stopPropagation),
+        dom.on('copy', stopPropagation),
+        dom.on('cut', stopPropagation),
+        dom.on('paste', stopPropagation),
         // On enter, focus on the input element.
         dom.onKeyDown({
           Enter : focusOnNew