fix(hl): use default hl groups

[disrupted]

I've changed the default highlight groups to default ones so that every colorscheme is supported out of the box.

[topaxi]

Thank you!

Just a quick question, do you know how these are different and why? Are these new?
Mostly wondering, I didn't know about these, and they do look different in my theme.

Happy to merge, just quickly wanted to know the actual difference :)

[topaxi]

Ah I assume the normal diagnostics are not the virtual text ones but ones shown in other contexts. I think this definitely makes sense, as in our case these are normal text.

[disrupted]

thanks for the feedback. tbh I just couldn't find any official documentation of the LspDiagnosticsVirtualTextError hl groups in Neovim :help. Perhaps these predate vim.diagnostic?

It looks like you were ready to merge this but it didn't go through. PR might need approval first?

edit: forgot about the readme. updated now

[topaxi]

Thanks for the update and contribution! <3