Fix Sonokai theme to better match original

[NickCondron]

The Sonokai theme had some inconsistencies, so I fixed some of them.

• Copied the palette exactly from https://github.com/sainnhe/sonokai/blob/master/autoload/sonokai.vim
• Used the following two resources to pick correct colors for different scopes:

1. https://www.sainnhe.dev/post/contributing-guide/#sonokai
2. https://github.com/sainnhe/sonokai/blob/master/colors/sonokai.vim

Edit: Changes I made as listed in the git commit:

• Make constants white (1)
• Make builtin variables purple (1)
• Make members orange (1)
• Make labels red (2)
• Make operators red (1)
• Make all punctuation grey (2)
• Make builtin functions and macros green (2)
• Make diff delta blue (2)
• Make cursor match bg4 (2)
• Make visible whitespace bg4 (2)

[the-mikedavis]

\cc @p4ymak what do you think about these colors (since you originally ported sonokai)?

[CptPotato]

I think this theme is based on my port of sonokai. I intentionally made some adjustments that I personally preferred.

But I'm fine with changing the theme here, the other version is still available on my repo.

[NickCondron]

Copying @p4ymak comments here because his comment was made in error on another PR:

@the-mikedavis sorry for long respond.

in my opinion, in general, the palette has become better. there are only two things I don't like: macros are no different from functions now, and parentheses and punctuation are too dim.

1. Sonokai colors constant-macros purple and function-macros green. Helix does not currently have scopes that differentiate the two kinds. Given that Helix does have a "function.macro" scope I went with green.
2. Sonokai clearly makes brackets and delimiters grey (https://github.com/sainnhe/sonokai/blob/e2e89497f178bec568a0a43cda651f0429ec8ec1/colors/sonokai.vim#L434). I understand that could be too dark for some tastes, but I think it makes sense to stick to the original as much as possible. I did realize that Sonokai makes special punctuation yellow, so I will amend the theme to add that.

[archseer]

Was the review fully addressed here?

[the-mikedavis]

I lost track of this PR a little - if you're still interested in updating these scopes could you rebase / merge master?

[NickCondron]

When I wrote this PR I was learning Helix. I no longer use the editor. Respectfully, I don't want to spend a whole lot of time on this. If it's an improvement and works I would be thrilled if it were merged. If not, hopefully someone else can expand on what I did.

I chose fidelity to the original theme where possible. However, I'm not the one who should decide on different color variations for secondary selections or other Helix-specific things. I tried to respect the more recent PRs. Also, I don't know if other scopes have been added/changed since I originally made the PR that could make this theme better.