enancement: Vim keybinds

[eamonburns]

First off, I want to say this project is awesome! Probably the best web-based language playground I have used.

I see this application is using CodeMirror, and I have also discovered the @replit/codemirror-vim package (linked to from the CodeMirror docs).

It looks like this package is pretty widely used (based on posts on the CodeMirror forum).

My request is to add Vim keybindings to the editor using this package.

Additionally, you could add custom keymaps to mirror NeoVim's default LSP keymaps.