Add xtask to generate the themes wiki page automatically

[hirschenberger]

It's a little bit distracting that in the themes wiki page all screenshots are of different size and show different code.

I think it would be possible to create an xtask that:

• iterates all themes
• creates a Document with some juicy soucecode
• renders it
• makes a screenshot
• generates the wiki md including the screenshots
• maybe a github hook to automize the whole process

[A-Walrus]

Is it possible to take screenshots within a GitHub CI VM? Do they even have any graphics like Xorg / Wayland?

[the-mikedavis]

Instead of doing this with screenshots / images, I think it would be wise to generate HTML or maybe SVGs. tree-sitter-highlight generates HTML and might be good inspiration. The theme could then just be translated to a stylesheet. With this change, we would most likely want to host the themes previews in the docs rather than the wiki. That would have the added bonus that the theme previews would be versioned: you could see what themes are available for the current release vs the master branch.

[the-mikedavis]

I'm not sure if this is how https://vimcolorschemes.com/ does it, but that might be good inspiration as well.

[hirschenberger]

There's a crate to-html that just needs a terminal with ansi-colors and renders that to html. So we wouldn't need X and it may work in CI.