Undo does not work for changes made to text format

[effieeee]

A user reported that undo (Ctrl+Z) is currently unable to reverse changes made to the text format (changes in font family or style). I was able to reproduce this on Windows 10 desktop app (v3.4.1), and web app (Chrome 83.0.4103.97), and it seems to happen regardless of how much or how little text I make changes to.

They also mentioned that they couldn't undo pasted text, though I was not able to reproduce that in particular.

[ningsongshen]

This would be more of an upstream issue for summernote. I did a quick look through their repository and found a few bits of information that describe how their undo function works:

• They record keydown history (not formatting), and undo character by character Support keydown event to record undo history summernote/summernote#3546
• The testing spec does not include anything for undoing formatting changes https://github.com/summernote/summernote/blob/master/test/base/module/Editor.spec.js

I can go ahead and create a feature request in the summernote repository to see if they can implement this.