Decouple BackDrop from modal (#32439)

* Create backdrop.js util

* revert breaking changes

remove PromiseTimout usage

revert class name

* one more test | change bundlewatch.config

* add config obj to backdrop helper | tests for rootElement | use transitionend helper

* Minor tweaks — Renaming

Co-authored-by: Rohit Sharma <rohit2sharma95@gmail.com>

build/build-plugins.js

@@ -65,7 +65,8 @@ const getConfigByPluginKey = pluginKey => {
     pluginKey === 'EventHandler' ||
     pluginKey === 'SelectorEngine' ||
     pluginKey === 'Util' ||
-    pluginKey === 'Sanitizer'
+    pluginKey === 'Sanitizer' ||
+    pluginKey === 'Backdrop'
   ) {
     return {
       external: []
@@ -133,7 +134,8 @@ const getConfigByPluginKey = pluginKey => {
 
 const utilObjects = new Set([
   'Util',
-  'Sanitizer'
+  'Sanitizer',
+  'Backdrop'
 ])
 
 const domObjects = new Set([