feat: Add text mode for showing alphanumeric keys as text

[80avin]

Context: I had to demo a vim session but seeing the alphanumeric keys as keycaps is very unintuitive.

This PR adds a text mode, in which, the text is shown as - text, not keycaps.

Also, it changes the default behaviour of / key, which was treated as ? in normal mode and / in shift mode, while in reality it is mostly opposite.

(ignore the low quality video - happened as artifact while converting mp4 to gif)

Since the feature was unasked, feel free to reject the PR.
And if you like the idea, I would request to add a proper "Vim mode" which renders all commands as vim renders shortcuts.

[JereNwa]

As for the "/" thing, there's a feature that you can enable that I think might help.

However, if you're going to add this feature, I recommend having the spaces actually show as spaces instead of having the " ﹈ " character appear.

[chan-yuu]

I really like this feature, could you please resolve the conflict of interest in this branch?

[80avin]

@JereNwa

• the Symbol setting doesn't help. It changes not only / / ? but also other symbol keys while the issue was / key was at wrong shift level. Example, in normal scenario, pressing / would type / but showed ?
• The ﹈ character was added delibrately as the usual space does not appear when pressed alone. In neovim, we commonly press two spaces and that would show in popup, which is visually indistuingishable.
  If you have better suggestion, let me know.

[80avin]

I have rebased the PR.