[Feature] Implement `E` and `e` emulation.

> Hello!
> 
> I am a big fan!
> 
> When will "e" roll in? I need it very much for textual work. Is there a specific reason why it is difficult to implement?
> 
> With thanks!!
> 
> _Originally posted by @gilbh in https://github.com/pit-ray/win-vind/discussions/3#discussioncomment-1912190_