feat: refactor vite styles plugin

[userquin]

This PR includes:

• simplify virtual logic: refactor logic to remove any virtual usage: using target mapping from .css to .sass + writing temporary SASS files when using SASS Variables (will solve missing sass source warnings and SSR problems when using Nuxt) ✔️ we only need to fix vue router warnings when running Nuxt with SSR enabled
• handle none and object styles notation at once
• include useViteFileImport in shared options
• docs: include similar hint to Vuetify docs in readme file

You can check the following repos and the corresponding PR:

• chore: don't write temp. sass files userquin/nuxt3-vuetify3-issue-15412#3 (Nuxt)
• chore: don't write temp. sass files userquin/vuetify-vite-modern-sass#3 (Vite)

supersedes #332

[userquin]

uhmm, with ?inline there is flickering in Nuxt dev server when refreshing page with SSR.

[userquin]

@KaelWD now it works in Vite and Nuxt with and without SSR (no vue-router warnings for virtual SASS files requests), updated linked repos PR if you want to check it (using same logic here).

[TechAkayy]

Thanks @userquin, I just tested modern sass api on my sample repo here - https://github.com/pinegrow/pg-vue-vuetify. Especially, when I work on vuetify with Vue Designer, sass updates use to be very sluggish. With sass modern api, I feel its pretty smooth, HMR is quite fast as well. Can't wait for this update to be out, especially for Nuxt app where more auto-magic happens.