feat(css)!: change default sass api to modern/modern-compiler

[hi-ogawa]

Description

Changing the default api for Vite 6 as described in #17728 (comment)

todo

• fix broken sourcemap fix(css): fix sass modern source map #17938
• docs

[stackblitz]

Run & review this pull request in StackBlitz Codeflow.

[sapphi-red]

/ecosystem-ci run

[vite-ecosystem-ci]

📝 Ran ecosystem CI on 27bd441: Open

suite	result	latest scheduled
astro	❌ failure	❌ failure
nuxt	❌ failure	✅ success
redwoodjs	❌ failure	❌ failure
remix	❌ failure	❌ failure
sveltekit	❌ failure	❌ failure
vike	❌ failure	❌ failure
vite-plugin-svelte	❌ failure	❌ failure
vitest	❌ failure	❌ failure

✅ analogjs, histoire, ladle, laravel, marko, previewjs, quasar, qwik, rakkas, storybook, unocss, vite-environment-examples, vite-plugin-pwa, vite-plugin-react, vite-plugin-react-swc, vite-plugin-vue, vite-setup-catalogue, vitepress, vuepress

[bluwy]

Updated the docs a bit. LGTM!