PB-170: TinyMCE Performance is very poor with multiple instances on Stage

- Add new implementation into Banner
- Ensure backwards compatibility with 3rd party appearances

Author: davemacaulay

app/code/Magento/PageBuilder/view/adminhtml/web/css/source/content-type/banner/_default.less

@@ -50,12 +50,10 @@
         }
 
         > .inline-wysiwyg {
-            overflow: auto;
-        }
-
-        > .mce-content-body {
+            line-height: 1.3;
             min-height: 50px;
             min-width: 10px;
+            overflow: auto;
 
             + .placeholder-text {
                 font-size: 14px;