Option to control copy/paste notification

From discord:

> I have also feature request. There is nice icon pops up when you cut or copy some text. However every kill command in Emacs triggers that icon to pop-up, which is kind of annoying. It would be nice to have option to disable that icon pop up.

Cc @zevlg

The issue names no files, tests, or entry points. Start by locating the iOS copy/paste notification and the handling of Emacs kill commands; done means providing a user option that controls whether the icon appears, with the existing behavior preserved by default.

Written by the indexing model from the issue text.