Add missing webpack exports

Add some entries to `package.json` to improve compatibility with webpack

- Add default `style` and `sass` exports as per webpack requirements
- Add `public/assets/styles/*` exports for CSS files
- Add `src/styles/*` exports for Scss files. Extension can be omitted
  to prevent linting issues with `stylelint`
- Add `*.scss` and `*.css` to "side effects" to prevent issues with
  tree-shaking

With this commit, it is possible to import styles with the same syntax
of v10 to prevent a breaking change in webpack based applications

Refs:
- https://webpack.js.org/guides/package-exports/
- 

Close Choices-js#1184

package.json

@@ -12,7 +12,9 @@
     ".": {
       "types": "./public/types/src/index.d.ts",
       "import": "./public/assets/scripts/choices.mjs",
-      "require": "./public/assets/scripts/choices.js"
+      "require": "./public/assets/scripts/choices.js",
+      "style": "./public/assets/styles/choices.css",
+      "sass": "./src/styles/choices.scss"
     },
     "./search-basic": {
       "types": "./public/types/src/index.d.ts",
@@ -23,9 +25,15 @@
       "types": "./public/types/src/index.d.ts",
       "import": "./public/assets/scripts/choices.search-none.mjs",
       "require": "./public/assets/scripts/choices.search-none.min.js"
-    }
+    },
+    "./public/assets/styles/*.css": "./public/assets/styles/*.css",
+    "./src/styles/*.scss": "./src/styles/*.scss",
+    "./src/styles/*": "./src/styles/*.scss"
   },
-  "sideEffects": false,
+  "sideEffects": [
+    "*.scss",
+    "*.css"
+  ],
   "scripts": {
     "start": "run-p js:watch css:watch",
     "build": "run-p js:build css:build",