refactor(css)!: always use sass compiler API (#19978)

Author: sapphi-red

config/shared-options.md

@@ -227,7 +227,7 @@ Note if an inline config is provided, Vite will not search for other PostCSS con
 Specify options to pass to CSS pre-processors. The file extensions are used as keys for the options. The supported options for each preprocessor can be found in their respective documentation:
 
 - `sass`/`scss`:
-  - Select the sass API to use with `api: "modern-compiler" | "modern"` (default `"modern-compiler"` if `sass-embedded` is installed, otherwise `"modern"`). For the best performance, it's recommended to use `api: "modern-compiler"` with the `sass-embedded` package.
+  - Uses `sass-embedded` if installed, otherwise uses `sass`. For the best performance, it's recommended to install the `sass-embedded` package.
   - [Options](https://sass-lang.com/documentation/js-api/interfaces/stringoptions/)
 - `less`: [Options](https://lesscss.org/usage/#less-options).
 - `styl`/`stylus`: Only [`define`](https://stylus-lang.com/docs/js.html#define-name-node) is supported, which can be passed as an object.
@@ -247,7 +247,6 @@ export default defineConfig({
         },
       },
       scss: {
-        api: 'modern-compiler', // or "modern"
         importers: [
           // ...
         ],