[WEB-876] fix: Multiple editor instances cause weird issues with Tippy (#4092)

* fix: tippy rendered properly when there are multiple editor instances

* enhancement: using cn to merge classes conditionally

packages/editor/extensions/src/extensions/slash-commands.tsx

@@ -330,7 +330,7 @@ const renderItems = () => {
       // @ts-ignore
       popup = tippy("body", {
         getReferenceClientRect: props.clientRect,
-        appendTo: () => document.querySelector("#editor-container"),
+        appendTo: () => document.querySelector(".active-editor") ?? document.querySelector("#editor-container"),
         content: component.element,
         showOnCreate: true,
         interactive: true,