Add vim setting to define the default vim mode

[typesend]

Summary

I would like my files open in insert mode by default, rather than normal mode.

  "vim": {
    "default_mode": "insert"
  },

For my specific use case, I suppose this feature is equivalent to one where I can use a keybinding to toggle the boolean "vim_mode" setting. However, I imagine folks may want to set any valid vim mode as their default. The default should continue to be normal mode.

For comparison, VS Code has at least one vim extension that supports this option:

"vim.startInInsertMode": true

[ConradIrwin]

Thanks for the idea! If you want to pair with me on this: https://calendly.com/conradirwin/pairing.

[croccifixio]

A configurable default vim mode would be really nice to have for those using the recently merged Helix support #19175 which added a new mode: helix_normal.