Use single file for extends (#3216)

* Use single file for extends

* Update changelog

test/utils.js

@@ -1,63 +1,64 @@
 module.exports = Object.freeze({
   SOURCES: [
-    `base/animations.sass`,
-    `base/generic.sass`,
-    `base/minireset.sass`,
+    `base/animations`,
+    `base/generic`,
+    `base/minireset`,
 
-    `components/breadcrumb.sass`,
-    `components/card.sass`,
-    `components/dropdown.sass`,
-    `components/level.sass`,
-    `components/media.sass`,
-    `components/menu.sass`,
-    `components/message.sass`,
-    `components/modal.sass`,
-    `components/navbar.sass`,
-    `components/pagination.sass`,
-    `components/panel.sass`,
-    `components/tabs.sass`,
+    `components/breadcrumb`,
+    `components/card`,
+    `components/dropdown`,
+    `components/level`,
+    `components/media`,
+    `components/menu`,
+    `components/message`,
+    `components/modal`,
+    `components/navbar`,
+    `components/pagination`,
+    `components/panel`,
+    `components/tabs`,
 
-    `elements/box.sass`,
-    `elements/button.sass`,
-    `elements/container.sass`,
-    `elements/content.sass`,
-    `elements/icon.sass`,
-    `elements/image.sass`,
-    `elements/notification.sass`,
-    `elements/other.sass`,
-    `elements/progress.sass`,
-    `elements/table.sass`,
-    `elements/tag.sass`,
-    `elements/title.sass`,
+    `elements/box`,
+    `elements/button`,
+    `elements/container`,
+    `elements/content`,
+    `elements/icon`,
+    `elements/image`,
+    `elements/notification`,
+    `elements/other`,
+    `elements/progress`,
+    `elements/table`,
+    `elements/tag`,
+    `elements/title`,
 
-    `form/checkbox-radio.sass`,
-    `form/file.sass`,
-    `form/input-textarea.sass`,
-    `form/select.sass`,
-    `form/tools.sass`,
+    `form/checkbox-radio`,
+    `form/file`,
+    `form/input-textarea`,
+    `form/select`,
+    `form/tools`,
 
-    `grid/columns.sass`,
-    `grid/tiles.sass`,
+    `grid/columns`,
+    `grid/tiles`,
 
-    `helpers/color.sass`,
-    `helpers/flexbox.sass`,
-    `helpers/float.sass`,
-    `helpers/other.sass`,
-    `helpers/overflow.sass`,
-    `helpers/position.sass`,
-    `helpers/spacing.sass`,
-    `helpers/typography.sass`,
-    `helpers/visibility.sass`,
+    `helpers/color`,
+    `helpers/flexbox`,
+    `helpers/float`,
+    `helpers/other`,
+    `helpers/overflow`,
+    `helpers/position`,
+    `helpers/spacing`,
+    `helpers/typography`,
+    `helpers/visibility`,
 
-    `layout/footer.sass`,
-    `layout/hero.sass`,
-    `layout/section.sass`,
+    `layout/footer`,
+    `layout/hero`,
+    `layout/section`,
 
-    `utilities/controls.sass`,
-    `utilities/derived-variables.sass`,
-    `utilities/functions.sass`,
-    `utilities/initial-variables.sass`,
-    `utilities/mixins.sass`,
+    `utilities/controls`,
+    `utilities/derived-variables`,
+    `utilities/extends`,
+    `utilities/functions`,
+    `utilities/initial-variables`,
+    `utilities/mixins`,
   ],
   buildCSS: (fn, name, options) => {
     try {