Add diff syntax highlight

[louim]

Hello! Here is a screenshot what a diff looks like in the Solarized Dark theme Here is the same diff in the Spinel theme

I added the required tokens to make it work with Spinel, based on the Solarized dark colors.

Result:

I'd be happy to adjust the colors to something more appropriate for the theme, if someone want to suggest what should be used.

[louim]

I have signed the CLA!

[vinistock]

Thank you very much for the contribution! Are these tokens only used when viewing git patches or do they also apply to solving conflicts?

Also, instead of using colours from a different theme, we should try to stick to the colours used in Spinel. We have red, green and blue for keywords, strings and local variables, respectively. Can we use those instead?

[vinistock]

Oh, I think you need to format the file. Running yarn run format should do the trick.

[louim]

@vinistock thanks! I updated the colors to use theme colors. Here's an example showcasing the changed color when used with git commit --verbose.

Are these tokens only used when viewing git patches or do they also apply to solving conflicts?

I think that VSCode uses special colors to highlight the in app merge and diffs. They do not seem affected by the theme itself.

I also had to remove the punctuation from tokenColors for the punctuation highlight to work correctly.

Before removing punctuation:

After removing punctuation:

Maybe we would then need to define more specific punctuation scopes?