Add granular CSS Modules options

[timneutkens]

Change in this PR

Adds granular options to switch on/off CSS module scoping for CSS features that are prefixed by default in Lightning CSS currently. For example animation, grid, and custom identifiers.

let { code, map, exports } = transform({
  // ...
  cssModules: {
    animation: true,
    grid: true,
    customIdents: true,
  }
});

The reason this is useful is that for example Webpack's CSS modules implementation does not do prefixing of grid. If you're migrating to Lightning CSS, like we're doing in Next.js / Turbopack it's helpful to disable the grid prefixing feature to ensure people have a smooth experience migrating.

Last test failure

The PR is mostly done, just one more case with animation: false where it somehow uses CustomIdent which in turn means it still prefixes.

PR feedback

I'm not proficient in writing Rust currently, using working on these smaller changes in Turbopack and other deps of Turbopack to learn as well, let me know if anything should be changed 👍

Improved assert_eq failure reports in tests

While investigating mismatches it was quite hard to read the assert_eq for these outputs when they mismatch. Added pretty_assertions to add much better diffs for these cases:

Before:

After:

[devongovett]

These should probably default to true like below.

[devongovett]

Suggested change

	dest.css_module.as_mut().map_or(false, |css_module| css_module.config.animation);
	dest.css_module.as_ref().map_or(false, |css_module| css_module.config.animation);

[devongovett]

write_dashed_ident already checks the dashed_idents option. I'm not sure that the custom_idents option also needs to affect dashed idents as well?

[devongovett]

need the check here too