[FIX] web_editor: make toolbar scrollable in note on mobile

Before this commit, the web_editor toolbar wasn't horizontally scrollable
and part ot the items were out of the screen area.

To fix this, we have to revert back the initial position on some elements.

addons/web_editor/static/src/scss/web_editor.common.scss

@@ -403,6 +403,14 @@ a.o_underline {
 }
 
 @include media-breakpoint-down(sm) {
+    odoo-wysiwyg-container {
+        .panel-heading.note-toolbar {
+            overflow-x: auto;
+        }
+        .btn-group {
+            position: static;
+        }
+    }
     // modal select media
     .o_technical_modal {
         // see template 'web_editor.FieldTextHtml.fullscreen'