build(vite): replace webpack with Vite, add Typescript (#1594)

BREAKING: mixins are no longer exported from the index (and will likely be converted to hooks)

postcss.config.js

@@ -1,10 +1,3 @@
 module.exports = {
-  plugins: [
-    require('postcss-import'),
-    require('autoprefixer'),
-    require('postcss-nested'),
-    require('cssnano')({
-      preset: 'default',
-    }),
-  ],
+  plugins: [require('autoprefixer'), require('postcss-nested')],
 }