Add idx to codeaction selector

[qRoC]

Add idx to codeaction selector

This allows you to quickly select an action from a list.

Current:

This PR:

[qRoC]

needs remove plenary dependency?

[stevearc]

Looks good! But yes, please remove the plenary dependency. vim.api.nvim_strwidth should function the same.

[qRoC]

@stevearc done

[stevearc]

Awesome, thanks!