Support tsconfig aliases in CSS @import

[bluwy]

Changes

Fix #6551 (take 2)
Supersedes #6626

This PR refactors vite-plugin-config-alias, and adds a config.createResolver patch that would make this plugin apply to CSS @import too. Even though this is a bit hacky, it's the only way to make it work completely.

Testing

#6812 added tests that previously caused regressions.

This PR also adds more tests for dev and build, and runs on Windows too.

Docs

n/a. Import aliases in the docs should already implicitly apply for style @import too, so I don't think this needs to be explicitly documented.

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Latest commit: d0dc54e

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[github-actions]

This PR is blocked because it contains a minor changeset. A reviewer will merge this at the next release if approved.

[Princesseuh]

Is there a world in which using a plugin like https://github.com/aleclarson/vite-tsconfig-paths would reduce the amount of code we need to do ourselves and potentially reduce maintenance work here?

[bluwy]

vite-tsconfig-paths actually has this issue too (aleclarson/vite-tsconfig-paths#41), but if it get fixed upstream, I think it makes sense to use the plugin. It's quite exhausting to maintain this 🥲

If the patch works in this PR, I can upstream the changes too.

[Princesseuh]

Looks good! Would love to see us use an upstream plugin for this in the future to reduce the maintenance burden though