feat: support ANSI themes

[smores56]

The current default theme is base16-ocean.dark, which as you can see below doesn't match the terminal colors by default:

If I load an 8-bit theme like this one from this neo-ansi repo, I currently see all black theming:

This is because ANSI is configured in .tmTheme files as #RR000000, a.k.a. the 8-bit color is in the red component and all other components, especially the Alpha, are 0x00. Assuming colors are 8-bit if the alpha is zero is suggested by syntect's author in this comment, and is implemented in bat already here. Given these precedents, I went ahead and implemented it, as seen below:

This implementation uses crossterm to write the escape sequences, which has a few benefits:

• We are already importing crossterm, so there are no new dependencies
• We have fewer magic constants, as crossterm provides them for us
• We make fewer string allocations, as we write directly to our output string this way instead of writing each line to a new string and then re-allocatiing

I think that ANSI themes are a better default for these kind of color-specific tools (since they always match the colors of the terminal), but there are no ANSI themes packed by default into syntect's ThemeSet::load_defaults that we use. Maybe a future PR could change to this ANSI theme from bat.

[sxyazi]

Awesome, this is the feature I've been wanting to add all along. Thank you for implementing it! I'll review it ASAP.

[sxyazi]

Looks good to me! Would you like to change the default to an ANSI theme in this PR as well?

I think it's quite reasonable as it not only makes Yazi more compatible with users' terminals but also potentially resolves #295.

[smores56]

Yeah, I totally agree. Just didn't want to do it without the author's permission. I'm not exactly sure where the ansi.tmTheme should go, my current location is yazi-config/preset/ansi.tmTheme, but yazi-plugin/preset/ansi.tmTheme also makes sense. Let me know if you have a preference.

[smores56]

I used the neo-ansi theme and not bat's ANSI theme since the bat theme was mostly black.

[smores56]

I'm happy if you're happy, feel free to squash and merge whenever! Thanks for the awesome file manager!

[sxyazi]

Thank you! Let me make some little changes.

[sxyazi]

Hi, I've made some changes:

• Add support for bold, italic, and underline
• Remove unnecessary ANSI sequence conversions - highlighting results are converted to ANSI sequences and then re-parsed into TUI components. Now it's just one step - from highlighted results to TUI components. This can save a lot of memory overhead and ANSI sequence parsing costs.
• Switch to the default theme of bat and port it to another separate crate yazi-prebuild. I've copied' bat's code for parsing colors and the issue with black text disappears.

Would you like to give it a review?