[Vite] Use CSS entry point

[manuelodelain]

Instead of import the main style file into the main entry js file we should load it directly as a Vite entry point.
See https://symfony-vite.pentatrion.com/guide/tips.html#css-file-entrypoints

Pros:

• use a single entry point for all the application. Remove the need to import it in main.js / simple.js / .storybook/preview.ts (shared.js should be deleted)
• remove the FOUC during development