Uppercase shortcut does not working.

[Teo-Cardoso]

The shortcut keys are shown as uppercase letters, however, when uppercase is enabled the shortcuts don't work. I see four ways of dealing with this:

1. Add the uppercase and keep the lowercase letters as well
2. Remove lowercase shortcuts and add the uppercase letters
3. Change the letters on the UI to lowercase and keep the shortcuts in lowercase letters
4. Don't change anything and keep it this way

[eduidl]

@Teo-Cardoso Thank you for your feedback! This is the default specification of the TUI library, textual, and I did not intend to make the display and behavior inconsistent. I'm going to choose the third options. I'm fixing this issue in https://github.com/eduidl/rtui/pull/4.

[eduidl]