refactor(commands): move util function to toolbox

[hinell]

I actually wanted to include this patch into #415 PR, but decided to go separately.

How to Test

N/A

Testing for Regressions

I have tested the following:

• Triggering keymaps from legendary.nvim in all modes (normal, insert, visual)
• Creating keymaps via legendary.nvim, then triggering via the keymap in all modes (normal, insert, visual)
• Triggering commands from legendary.nvim in all modes (normal, insert, visual)
• Creating commands via legendary.nvim, then running the command manually from the command line
• augroup/autocmds created through legendary.nvim work correctly

[mrjones2014]

What's the purpose of this PR?

[hinell]

@mrjones2014 Refactoring. That function might be used elsewhere, so it's logical to keep it in tool box.

[mrjones2014]

That function might be used elsewhere

But it isn't currently. We can move it if/when it's needed.

[mrjones2014]

Toolbox is supposed to be more for end-user utilities, this is an internal parser.