The web engine has some logic to be able to copy-paste content from a Flutter app, which is using a now outdated/deprecated API (document.execCommand) as a fallback for browsers that didn't implement the standard API.

We only use the following methods from the standard Clipboard API:

• writeText, to put content into the users' clipboard (widely available, since Safari 13.4 (~March 2020))
• readText, to read content from the users' clipboard (widely available, since Firefox 125 (~April 2024))

It seems that soon we'll be able to remove the execCommand fallback, and all the scaffolding to make it work.

See ExecCommand* strategy classes here:

• https://github.com/flutter/engine/blob/0b56cb8de79e28c4bb58e98129011ca7e684e12e/lib/web_ui/lib/src/engine/clipboard.dart

(PS: We should also remove the execCommand definition from the engine's dom.dart!)

Closes: #48581