build(style): support importing styles in Sass (#2555)

* Support importing styles in SASS

This gives consumers more flexibility to manipulate the base CSS. For example, forcing the styles under a CSS layer

```scss
@layer third-party-libs {
  @import 'pkg:react-day-picker/styles.module';
}
```

Signed-off-by: George <[email protected]>

* Remove .css extension from sass export

Sass requires that CSS imports do not have the extension in the URL. Otherwise, it will be interpreted as a runtime import

---------

Signed-off-by: George <[email protected]>

package.json

@@ -52,6 +52,9 @@
         "default": "./dist/cjs/locale.js"
       }
     },
+    "./style": {
+      "sass": "./src/style.css"
+    },
     "./style.css": {
       "style": {
         "default": "./src/style.css"
@@ -65,6 +68,9 @@
         "default": "./src/style.css"
       }
     },
+    "./style.module": {
+      "sass": "./src/style.module.css"
+    },
     "./style.module.css": {
       "style": {
         "default": "./src/style.module.css"